Conference Agenda

Optical sensing exploiting plasmonics and other types of surface waves provides exceptional performance for chemical and biological detection due to its high sensitivity and real-time capabilities. This study explores the integration of thin films with plasmonic, specifically leveraging metallic and dielectric nano structures, fabricated through sputtering and colloidal synthesis techniques. Advanced surface wave excitations such as localized surface plasmon resonances (SPR), Tamm Plasmon Polaritons (TPP), Bloch surface waves, and surface plasmon polaritons (SPP) are used to amplify sensor performance. Simulations and experimental data show that these nanostructured coatings significantly enhance electromagnetic field confinement, leading to improved detection limits and sensor robustness, showcasing promising applications in environmental monitoring, gas detection, and biomedical diagnostics.

The range of applications using gold nanostructures for optical sensing increases rapidly, primarily utilizing the local surface plasmon resonance effect that increases the sensitivity. Among electrochemical and colloid chemical preparations, one of the most effective and widely used ways of preparing gold nanoparticles is sputtering or evaporation followed by thermal annealing. A broad range of recipes exists in the literature; however, the optimal parameters depend greatly on the initial thickness of the gold layer, the temperature profile, or the substrate material. We show that combinatorial preparation and in situ ellipsometry are powerful ways to optimize the amount of material and the temperature profile, respectively. We show that the sensitivity can be enhanced even more when ordered periodic gold nanostructures are used, one of the simplest forms of which is a gold grating. The limit of detection values for the ambient and overlayer were calculated using finite element optical simulations.

Achieving optimal wine quality depends on precise harvest timing, a traditionally laborious and subjective task. To address this challenge, this study proposes the integration of advanced sensing technologies. Proximal sensors, such as the Multiplex fluorescence sensor, and remote sensing via UAV-based imaging are combined to provide a comprehensive assessment of grape phenolic maturity. This integrated approach aims to deliver spatially explicit information, enabling accurate and efficient monitoring of grape quality and ultimately, optimizing wine production.

Aimed at enhancing the sensitivity, we develop an integrated optically pumped magnetometer (OPM) with the dual-beam scheme. Additionally, we explore the application of this sensor for magnetic particle detection and propose a method to estimate the rotation frequency of magnetic particles. Through experimental analysis, we establish a correlation between the rotation frequency and the flow rate, which enables the flow rate measurement.

This paper presents a novel optical-comb-based refractive index sensor that simultaneously achieves high-sensitivity and high-precision by combining THz-comb-based frequency multiplication with active-dummy temperature compensation in a dual-comb configuration. In this approach, a little RI-induced shift of the comb mode spacing (frep) is frequency-multiplied via THz frequency comb, while the dual-comb scheme compensates for temperature drift in frep. Experimental results demonstrate a 3100-fold improvement in RI sensitivity and a 10-fold enhancement in measurement precision.

We present a new microscopic theory for wavefront shaping in complex media, extending the classical radiative transfer framework to describe the coherent propagation of structured waves. This formalism captures, for the first time, the full spatial structure and transmission properties of scattering eigenstates, revealing how their intensity profiles depend on the medium’s geometry. It remains accurate beyond the diffusive regime and naturally incorporates experimental complexities such as absorption and partial channel control. This framework offers powerful tools to understand and manipulate wave transport in complex photonic systems.

Strong Anderson Localization manifests itself as an interference wave phenomenon, potentially leading to completely localized states under infinite extension. We propose a framework for characterizing light transmission through three-dimensional high-refractive amorphous materials, showcasing both localization and photonic band gaps (PBG). Leveraging advanced numerical techniques and recent advancements in Finite-Difference Time Domain (FDTD) simulations, we explore how light behaves in complex dielectric materials and how these effects interact near the bandgap.

State-of-the-art computational methods combined with common idealized structural models provide an incomplete understanding of experimental observations on real nanostructures, since manufacturing introduces unavoidable deviations from the design. We propose to close this knowledge gap by using the real structure of a manufactured nanostructure as input in computations to obtain a realistic comparison with measurements on the same nanostructure. We demonstrate this approach by computing the transmission spectrum based on the structure of a real photonic bandgap crystal, as previously obtained by synchrotron X-ray imaging. This spectrum is complex with among others significant frequency speckle and shrinking of the stopband, which can not be predicted by a Utopian model with perfectly round pores. Our method provides essential insight in the effects of manufacturing deviations on the optical properties of real nanostructures.

Fruitful analogies exist between waves like light or sound that propagate in mesoscopic photonic or phononic metamaterials and the elementary excitations in atomic crystals like phonons, electron and spin waves. A peculiar class of wave transport is discretized transport with hopping in all three dimensions on superlattices, as demonstrated in phonons, electrons and spins, but not yet for light. Here, a superlattice is a periodic arrangement of a supercell that consists itself of multiple unit cells of an underlying crystal structure. In this work, we experimentally observe light waves propagating by hopping between neighbouring cavities along high-symmetry Cartesian directions in space. The hopping transport leads to the appearance of defect bands in the 3D photonic band gap, as theoretically identified by scaling and machine learning methods. Cartesian light is a completely new mode of light propagation (e.g., different from CROWs) that opens the door to a plethora of applications.

This study theoretically demonstrates the use of subwavelength structures to create a metamaterial (MM) for birefringent capping on a one-dimensional photonic crystal (1DPC). The MM-terminated 1DPC can simultaneously support both transverse electric (TE) and magnetic (TM) surface modes within the visible to near-infrared (VIS-NIR) range.

The benefits in terms of cost efficiency and versatility achieved through the development of flexible and stretchable electronics and optoelectronics have greatly fueled the exploration of flexible photonic technologies. Introducing mechanical flexibility to photonic structures enables novel functionalities, further broadening their range of applications. Alongside advancements in flexible photonics based on organic platforms, an emerging approach is gaining attention, emphasizing the use of inorganic, all-glass ultra-thin structures. For oxide-based materials, their intrinsic properties, such as transparency, high thermal resistance, and chemical stability, can be harnessed within appropriate systems.

We present flexible SiO2/HfO2 one-dimensional photonic crystals, fabricated via radio frequency sputtering. These systems exhibit a pronounced dependence of their optical properties on the angle of light incidence, particularly demonstrating a blue-shift of the stopband and a narrowing of the reflectance window. However, the most remarkable finding lies in the experimental evidence showing that even after breakage, with visible cracks forming in the flexible glass, the multilayer structures largely retain their integrity. This positions them as promising candidates for flexible photonic applications due to their robust optical, thermal, and mechanical stability.

This research is supported by the projects: CANVAS, LEMAQUME-QuantERA, Project PNRR NFFA-DI IR0000015, PRIN 2022 PNRR P2022YM8J3 - NANOSEES, HORIZON-TMA-MSCA-DN Met2Adapt.

This work focuses on the optimization of a compact square prismatic single stage solar concentrator to be realized either with BK7 glass or Silopren plastic. Zemax software is used to simulate and optimize the optical surfaces. The concentrator consists of a spherical surface atop a parallelepiped, placed above an inverted truncated pyramid. The simulated optical efficiency, without any antireflective coating, ranges between 89% and 96%, with a concentration factor of 400 suns, and an acceptance angle ranging between 0.8° and 1.0°. The collection surface is 5x5 mm2, and the total concentrator height is 10 mm. The optics has been designed to operate in micro-concentrating photovoltaic modules.

This study investigates thiophene oligomers as fluorophores incorporated within poly(methyl methacrylate) (PMMA) films, fabricated using slot die coating. This versatile technique ensures high optical quality and excellent reproducibility of the deposited films, provided reliable coating parameters are established. Optimized coating conditions yielded highly fluorescent films with a thickness of 30 µm, which were then employed to develop Luminescent Solar Concentrators (LSCs). Electrical characterization, conducted in accordance with standard procedures, revealed that oligomers exhibiting larger Stokes shifts demonstrated superior device performance due to reduced re-absorption losses. These findings underscore the potential of thiophene oligomers for efficient LSC applications.

Ridge low loss (0.16±0.02 dB/cm) waveguides were fabricated in Pr,Gd:LiYF4 epitaxial layers by precision diamond-saw dicing. The red waveguide laser generated 504 mW at 639.7 nm with a slope efficiency of 57.8%, a linear polarization and a laser threshold of 34 mW. Laser operation in the orange and deep red was also demonstrated.

J-aggregates thin films of cyanine dyes are very attractive organic nanomaterials formed by highly ordered assembly of supramolecular organic structures. These films show unique spectroscopic properties, making them promising candidates for integration into advanced electronic and photonic devices. Their spectra show very narrow resonances, resulting in spectral regions with high refractive index, comparable to semiconductors, and negative permittivity, similar to metals. This study focuses on the characterization of the optical properties of cyanine J-aggregates thin films, including refractive index and permittivity, in a wide spectral range from visible to near infrared wavelengths. Our findings highlight the potential of these structures for the development of sustainable photonic devices.

This study presents a technique for measuring the thermal conductivity of materials based on the strong reflectance change caused by the insulator-to-metal transition in VO₂ thin films. Unlike conventional pump-probe and frequency-domain thermoreflectance techniques, this approach is based on steady-state optical microscopy. The presented technique involves imaging the metallic domain induced by a continuous-wave laser beam illumination on the VO₂ surface as a function of laser intensity. By fitting the radius-intensity relationship with a theoretical model developed for this purpose, the thermal conductivities of three materials (silica glass, sapphire, and silicon) are accurately determined, yielding values in good agreement with the tabulated data.

We report a theoretical and experimental investigation of far-detuned intramodal (FWM) in the fundamental mode of optical microfibers (OMF) depending on their diameter. We demonstrate that the signal wavelength can be tuned over a wide spectral range simply by varying the OMF diameter. Using a pump at 1064 nm, signal wavelengths ranging from around 750 to 950 nm are generating by adjusting the OMF diameter from approximately 8.5 to 6.5 µm.

This work aims to optimize the Kerr effect in optical nanofibers made from various glass materials with refractive indices close to that of silica and immersed in acetone. Key factors considered include the nanofiber diameter, the optical properties of the core material, and the effective area of the fundamental HE11 mode, both within the core and in the surrounding medium. The study highlights the influence of these parameters on enhancing the nonlinear optical response through the evanescent field.

We present numerical calculations and experimental measurements of Brillouin scattering efficiency in a nanofiber gas cell. The results demonstrate highly efficient nonlinear conversion within the nanofiber gas cell

Optical nanofibers (ONFs) made from fluorophosphate glass (OHARA - FPM) enable strong confinement, low losses, and enhanced evanescent fields for nonlinear optics. We show that the HE11 mode achieves high Raman gain (11.62 m−1·W−1) in a compact 10 cm ONF with a 300 nm radius. These results optimize ONF fabrication, lower the Raman threshold, and expand the Raman effect’s operational range.

Interferometry has long been used to measure the phase of light signals. Combined with a heterodyne detection scheme, it allows to simultaneously and unambiguously record amplitude and phase variations. In this work, we exploit these well-known techniques to evaluate the nonlinear phase induced by the optical Kerr effect during the propagation of a laser pulse in a nonlinear medium. We show that the nonlinear index can easily be retrieved when the accumulated phase remains small, but counter-intuitive results can be observed at higher powers.

Wavefront shaping allows focusing and imaging at depth in disordered media such as biological tissues, exploiting the ability to control multiply scattered light. Many so-called guide-star mechanisms have been investigated to deliver light and image non-invasively, among which incoherent processes such as non-linear fluorescence feedback. However, the most common microscopy contrast mechanism, linear fluorescence, remains extremely challenging. I will discuss some of our recent works, exploiting signal processing and machine learning frameworks, to recover images behind scattering layers exploiting linear fluorescence.

Structured illumination microscopy (SIM) is a technique that employs non-uniform illumination to shift spatial frequencies that are normally unobservable into the region of the non-zero optical transfer function (OTF). Several images are combined to reconstruct these spatial frequencies, yielding up to twofold increase in resolution beyond the diffraction limit. However, the reconstruction process is affected by noise, and spatial frequencies can only be estimated with a certain precision and accuracy that depends on the procedure used. The spectral signal-to-noise ratio (SSNR) serves as an indicator of the possible quality of a reconstruction. Conventional SIM reconstruction is based on a least-squares estimate; while this approach yields high SSNR, it is performed in the Fourier domain and assumes uniform imaging conditions (illumination brightness, modulation depth, aberration coefficients) across the field of view (FOV). In large FOVs, this assumption is often violated, resulting in artifacts. An existing spatial-domain procedure produces low SSNR at high spatial frequencies, rendering these effectively unresolvable under low-light conditions. In this work, we present a local SIM reconstruction procedure with an order-of-magnitude higher SSNR. We demonstrate that it nearly achieves the SSNR of Fourier domain reconstruction, and we also show that further improvement is not possible.

Novel formulas have been derived for the primary spherical aberration, coma and axial color of systems of thin lenses in contact. Even in complex optical systems, groups of lenses can be modelled as thin lenses in contact. The new mathematical formalism helps explaining significant qualitative properties of the lens design landscape.

Distortion is a common annoyance in optical imaging. Learning from computer vision, many distortion correction algorithms are developed, mostly based on the Brown-Conrady model. An analysis of the field dependence of aberrations in terms of the zero aberration points in the field of view, the so-called nodes, provides another inroad to study distortion. Using the Nodal Aberration Theory, we show that the distortion field is the gradient of a scalar field. Structural changes in the distortion field are characterized by a complex sequence of creation, annihilation and reorganization of up to five nodes driven by tilt and decenter misalignments of the optical components. This description can be fruitfully applied in alignment protocols for complex optical systems, in image registration of multi-color localization microscopy, and of correlative light and electron microscopy.

Elevation topography equipment measures freeform surfaces by representing the surface with elevation maps, maximum curvature, minimum curvature, mean curvature, and Gaussian curvature. From a geodetic point of view, every regular point on a parametric surface can be described as a function of the principal curvatures and the local torsion concerning a reference path at each point. Here, we present some fundamentals required to create these density maps to represent the absolute torsion and the local conic constant of all points on a regular freeform surface.

The demand for 100% inspection is increasing due to rising quality requirements in manufacturing. Multiwavelength Digital Holography (MDH) has emerged as a promising sensing technology capable of achieving both high throughput and high resolution. However, despite its potential, MDH has not yet been widely adopted in commercial metrology applications.

One of the key challenges in MDH system design is minimizing noise in the laser-illuminated optical imaging system. Due to the high coherence of laser light, digital holography systems are particularly sensitive to particle contamination and internal reflections within optical components.

We address this challenge by introducing a phase randomizing mirror (PRM) that controls coherent length by dynamically modulating the spatial profile of the illumination. Compared to conventional mechanical modulation methods, the PRM operates at significantly higher frequencies, enabling shorter exposure times. This results in a system that is not only high-throughput but also more resilient to environmental vibrations.

In this presentation, we will discuss the impact of the PRM on our newly developed phase-shifting digital holography system and demonstrate its application in real-world inspection scenarios.

Zernike polynomials are widely used to approximate optical aberrations and represent them in a compact, yet sufficiently accurate way. They are essential in precision optical manufacturing to characterize surface figure errors and wavefront aberrations of optical systems measured by interferometers or wavefront sensors. Zernike polynomials also describe freeform surfaces in optical design and are used in adaptive optics to correct for dynamic aberrations such as atmospheric turbulence.

The aberration coefficients of the polynomials are typically presented in tables or simple bar graphs that can be difficult to interpret at first glance. This work presents intuitive visualizations of Zernike aberrations that emphasize the magnitude and orientation of the dominant terms. Depending on the polynomial degree of the approximation, we use bubble plots or heat maps to represent low-order and mid-spatial frequency terms, respectively. In addition, we propose an alternative definition for the angular orientation of the paired polynomials with azimuthal orders m ≠ 0.

These graphical tools provide immediate visual feedback, benefiting tasks such as aberration compensator adjustment, real-time wavefront monitoring, and optical alignment. They can also improve the clarity of acceptance reports and measurement certificates.

We present a calibration method that correlates in-line measurement results from a digital holographic microscope (DHM) integrated into a two-photon polymerisation system (TPP) with offline results from a high-resolution laser scanning microscope (LSM). Our findings indicate that a single calibration step for a specific polymer is sufficient to reliably monitor the fabrication of various structures. In future, this approach will make it possible to adapt the production process to the manufactured structure geometry in real time.

Conventional interferometers provide uniform phase sensitivity across the measurement range. However, for applications involving small phase changes, amplifying the response within a specific phase range—at the expense of reduced sensitivity elsewhere—can be advantageous. A key example is the Gires-Tournois etalon, used in gravitational wave interferometers. In this work, we introduce an ultrasensitive phase measurement system based on time-holographic recording with a conventional Mach-Zehnder interferometer, operated near the intensity minimum at the dark output port. Phase fluctuations in the milliradian range around this point are converted into rad-sized dark output phases, with amplification factors exceeding 1,000. The adjustable imbalance between the interferometer arms controls this magnification, which is revealed by heterodyning the output with a frequency-shifted beam. Phase is digitally retrieved from the time-hologram using Fourier processing, with noise subtraction for correction. The system achieves phase sensitivities better than λ/3,000, enabling sub-nanometer precision for dimensional measurements. This versatile platform provides powerful tools for ultrasensitive phase measurements in a wide range of scientific and technological applications.

In this work we investigate the efficiency and accuracy of different perturbation methods, for the important case of a 1D periodic grating. These methods are potentially important in the study of the influence on optical performance of mid-spatial frequency errors on the surfaces of optical components.

The scope is limited to reflective optical systems. The perturbation methods are based on the Rayleigh hypothesis, boundary integral equations and volume integral equations. The Padé approximant is used to improve the convergence of the perturbation series. Results for a specific grating are included in a to be published paper and will be shown during the presentation.

Ptychography is a powerful computational imaging technique that

reconstructs both the complex object function and the illumination probe from

overlapping diffraction patterns. While it provides high-resolution, aberrationcorrected

imaging, its reliance on stepwise mechanical scanning limits acquisition

speed. In this work, we propose a fly-scan ptychographic approach that

enables continuous sample translation along arbitrary trajectories, significantly

reducing measurement time. To account for motion-induced decoherence, we

incorporate an object mode decomposition model combined with automatic differentiation

for accurate trajectory correction. This method enables diffractionlimited

reconstructions without the need for high-speed tracking, allowing fast

and precise measurements using standard ptychographic setups.

Semiconductor lasers are very sensitive to optical feedback. Here we study experimentally the effect of optical feedback on the spatial coherence of a diode laser using the speckle technique. Speckle is a noisy structure arising from the interference of coherent waves as they propagate through a diffusive medium. Using a multimode fibre as the diffusive medium, we observe that, during the laser turn-on, without feedback, the speckle contrast increases gradually (revealing a gradual increase in spatial coherence), but, with sufficiently strong feedback, the speckle contrast increases sharply (revealing an abrupt increase in spatial coherence). For pump currents above the threshold, high-contrast regions alternate with low-contrast regions. We also observe that, under appropriate current modulation, high-contrast regions are suppressed. Our findings may find application in laser-based illumination systems, because optical feedback can be used in combination with current modulation to reduce speckles over a wide range of pump currents.

We study the relaxation behavior of an optical cavity with

memory in its nonlinear response. We show that the relaxation time of

the optical cavity with memory is mostly dominated by the timescale

of the thermal relaxation of the nonlinearity. However, when crossing

a bifurcation into the bistable regime, we observe slowing down of the

optical response by several orders of magnitude compared to the ther-

mal relaxation time. Experimentally, this slowing down was verified

using an oil-filled cavity.

The ability to detect near infrared light has important applications in telecoms, medical diagnostics and remote sensing. Traditional free-space up-conversion systems based on bulk crystals are not suitable for integration purposes, due to their large footprint. Here, we employ a nonlocal dielectric metasurface as an ultra-thin up-converter, by exploiting quasi-bound states in the continuum to increase the conversion efficiency of the nonlinear process.

We demonstrate a quantum interface that simultaneously converts the wavelength, bandwidth, and duration of single-photon-level pulses, enabling compatibility between disparate quantum systems. Using difference frequency generation in a lithium niobate waveguide driven by a highly chirped pump, we transform pulses from 798 nm, 5 GHz, 150 ps (quantum dot-like) to 1300 nm, 35 GHz, < 25 ps (telecom standard). This nonlinear optical time lens achieves over 80% internal conversion efficiency and compresses output pulses below detector resolution. The device offers a compact solution for integrating quantum emitters, memories, and telecom networks, with potential for further pulse shape control.

We present experimental and theoretical representation of quantum-like Schrödinger's cat states, by exploiting orbital angular momentum of the light. We investigated complex superposition as 3-Cat, 6-Cat and Fock-Cat states.

We developed an array of quantum detectors based on superconducting nanowires to allow two-photon-excited fluorescence in-vivo imaging of mouse brain vasculature working completely in the short wave infrared (SWIR) region of the spectrum, achieving an imaging depth of up to 900 um.

Optical trapping with structured optical fibers is reported for five species of the Pseudomonas genus. Contactless trapping at low intensities was realized with 3D printed Fresnel lens fibers and an original fiber emitting a tightly focused annular beam. Specific swimming features and the behavior of trapped bacteria of the investigated species are compared applying different numerical methods.

Light-based technologies, including lasers and LEDs, are widely utilized in various medical applications. Among these, low-fluence and prolonged irradiation in the visible (VIS) and near-infrared (NIR) spectral regions have demonstrated significant clinical benefits, such as reducing inflammation and pain, as well as stimulating regenerative processes. To investigate the underlying mechanisms of these therapeutic effects, we examined the responses behaviour of fibroblasts and keratinocytes following non-contact irradiation with a 420 nm LED at varying fluences (4–40 J/cm²). Post-treatment analysis was conducted using confocal and electron microscopy, Micro-Raman spectroscopy, cell metabolism and proliferation assays, as well as patch-clamp recordings. Our findings revealed fluence- and cell type-dependent modulation of metabolism, cytochrome C redox state, and membrane ionic currents. In conclusion, these findings pave the way for the design of photonics-based medical devices capable of achieving targeted effects on specific cell groups, thereby addressing particular medical challenges [1-4].

Addressing the limitations of animal models in biomedical research, we introduce a hierarchical manufacturing method for creating anatomical phantoms using water-in-elastomer micro-emulsions.

The building blocks are water-in-elastomer micro-emulsions made of a continuous phase of hydrophobic polydimethylsiloxane (PDMS) and micro-droplets of hydrophilic solutions of various dyes and other contrast agents. This material inherits some properties from the elastomeric matrix, such as the speed of sound and acoustic attenuation coefficient, some from the hydrophilic inclusions, such as the optical absorbance, and some from their overall ultrastructure, such as the intensity of optical scattering. The final material

provides independently tunable, tissue-mimicking characteristics in the relevant ranges of optical excitation and acoustic detection for PAI.

This approach addresses the cost, ethical, and technical limitations of animal models, providing a reliable alternative for multimodal imaging and artificial intelligence development, particularly in photoacoustic imaging.

Reducing invasiveness is key in developing modern endoscopes for imaging samples in hard-to-reach areas. This can be achieved using multimode fibers. Compressive sensing algorithms can be applied to multimode fiber imaging to reduce the imaging speed. These algorithms utilize a sub-Nyquist set of patterns while allowing to super-resolve the sample. The patterns must be uncorrelated, which is typically achieved by mechanically scanning the input beam across a multimode fiber. We demonstrated a setup combining a super-continuum laser and a monochromator to obtain wavelength-dependent uncorrelated speckles, removing the need for mechanical scanning. With compressive sensing algorithms, binary samples were reconstructed up to 95% faster compared with traditional methods. We expand our setup to incorporate broadband illumination, which is expected to further increase imaging speed and spatial resolution, paving a way for a compact, real-time imaging device.

Interferometric diffuse optics (iDO) enables non-invasive measurement of deep tissue blood flow without requiring photon-counting detectors. Due to hardware constraints, achieving both optical properties and depth-dependent dynamics within a single modality remains a challenge for iDO. We present a simple method based on frequency-modulated light scattering that overcomes this limitation.

UltraFast Innovations (UFI®) develops advanced tools for

ultrafast optical science, including compact XUV beamlines and highcontrast

autocorrelators. Our systems cover broad temporal domains from

nanoseconds to attoseconds. Key technologies include the TUNDRA®

autocorrelator, the NEPAL high-harmonics generation chamber, and the

SAVANNA post-compression stage. Recent high-power upgrades support

extreme laser conditions and enable the generation of few-cycle pulses,

pushing the boundaries of tabletop ultrafast science.

This work presents a superconducting microwave resonator that is

both frequency tunable and compatible with photolithography. This design is

well-suited for integration with electro-optic devices. We demonstrate tuning

ranges exceeding 500 MHz, using a bulk permanent magnet, and 100 MHz,

using planar coils, under moderate magnetic fields (below 5 mT).

In classical widefield microscopy, the resolution is limited by diffraction. We aim to overcome this limit using photon antibunching - a quantum property of fluorescence emission. Using pulsed laser excitation, with a pulse time much smaller, and the time between the pulses much longer than the fluorescence lifetime, we ensure that each fluorophore emits at most one photon per excitation cycle, as introduced by [1]. We synchronize this pulsed excitation with single-photon avalanche diode (SPAD) detection with a large array of 512x512 pixels allowing for wide field imaging. When two pixels detect a photon in the same frame, this means these photons originate from separate emitters. We will show that by analysing the spatial correlations between the pixels, a potential resolution improvement by a factor 2 can be achieved. We validate the method by simulation and apply it to experimental data.

[1] Schwartz, O., Oron, D. Improved resolution in fluorescence microscopy using quantum correlations. Phys. Rev. A 85, 033812 (2012).

uperresolution microscopy has transformed biological imaging, yet coherent nonlinear microscopy has not achieved similar resolution advances. Here, we apply image scanning microscopy (ISM) to coherent anti-Stokes Raman scattering (CARS), achieving resolution enhancement of ~1.5-2x. In ISM, each camera pixel captures a magnified image of the excitation spot, acting like an array of pinholes, and these signals combine to yield a higher-resolution image while maintain total signal. Adapting ISM to coherent imaging requires precise information of both the amplitude and phase of the signal. Our approach integrates CARS-ISM with an inline interferometer to retrieve phase. A 4f pulse shaper controls dispersion and phase-stepping of a reference. We generate the pump and Stokes beams with a Ti:Sapphire laser and synchronously pumped optical parametric oscillator, and obtain superresolved CARS images of the C-H stretch band.

The resulting images capture lipid droplets and other organelles at improved resolution compared to standard CARS. Crucially, the spatial variation in CARS phase, reflecting the local ratio between resonant and nonresonant contributions, enhances contrast. Tests with polymer grating targets confirm that ISM provides a ~1.5-fold resolution gain without advanced processing, indicating potential for further improvement and broad applicability in coherent nonlinear microscopy, including epi-detection setups.

We investigated the efficiency limitations of second-harmonic generation (SHG) in spliced optically poled Corning HI980 fiber segments. Although theory predicts quadratic growth with segment number, experiments show nearly linear efficiency scaling. Using a continuous wave model (CW), we demonstrate this subquadratic behavior primarily stems from random longitudinal shifts between quasi-phase-matching (QPM) regions in spliced segments. Further investigations through coupled generalized nonlinear Schrödinger equations (coupled GNLSEs) confirm fundamental frequency (FF) power depletion through Raman scattering and spectral broadening during propagation. Our numerical simulations successfully reproduced experimental spectral measurements, validating the model's accuracy. For the first time, we report the effective quadratic nonlinear coefficient induced by optical poling in this fiber: d_eff=9×10^(-4 ) pm/V.

We experiment a fast, localized, and fully optical erasure procedure for photorefractive solitonic waveguides written in lithium niobate on insulator (LNOI) thin films. This method enables real-time reconfiguration of self-written optical circuits by exploiting photovoltaic field-driven charge redistribution.

We study the polarization properties of blackbody radiation under Lorentz transformations. We especially show that the degree of polarization of blackbody radiation changes in such relativistic transformations, contrary to the Lorentz invariance of the degree of polarization of transverse fields. Our work provides a deeper understanding of relativistic effects on blackbody radiation and may find use in astrophysics and cosmology.

A polarization-independent reflective grism, consisting of a polarization-independent total-internal-reflection grating and a prism, can provide a large bandwidth and linear dispersion. It has promising potential applications for next-generation wavelength-selective switches (WSS). We have fabricated a grism of a line density of 1710 lines/mm. The average diffraction efficiency is 95.14% for TE and TM polarizations over the C-band (1523-1575 nm).

Through the fluorescence characteristics of polyethylene naphthalate (PEN) material under short-wavelength excitation, a boradband light source of visible wavelengths can be generated. By combining this with the white-light source, we propose the design of a simple birefringent PEN sensor, utilized in a white-light polarization interferometer for the dynamic measurement of ethanol volatilization. Based on these experimental observations, the application of detecting variations in liquid refractive index can be validated.

A study of an Eocene fish fossil using portable XRF revealed distinct geochemical differences between the fossil and surrounding sediment. Elements like uranium, yttrium, arsenic, and phosphorus were found only in the fossil, while calcium and iron appeared in both regions. These patterns point to selective elemental incorporation during early fossilization and diagenesis processes. The results highlight XRF's usefulness in verifying fossil authenticity, provenance and understanding the chemical processes during fossilization.

This work studies the influence of an Erbium-Doped Fiber Amplifier (EDFA) on the phase variation of light in an optical fiber. To this end, the state of polarization (SOP) was measured as a function of optical power by adjusting the EDFA amplification, for two different laser output powers (2 dBm and 5 dBm). Results show that phase variation correlates with changes in optical power in both cases.

Distributed Acoustic Sensing (DAS) leverages the sensitivity of optical fibers to detect environmental vibrations. This study demonstrates the capability of DAS to identify and characterize the acoustic signatures of passing vessels, highlighting its potential to enhance maritime surveillance and monitoring.

Optical clocks based on trapped ions are highly stable frequency standards with applications in navigation, fundamental physics tests, and chronometric geodesy. Hence, ion traps are a key component for ion-based quantum technology applications. To achieve greater scalability and laser pointing stability, it is crucial to integrate nanophotonics monolithically into ion trap architectures. Addressing and manipulating the ions requires wavelengths ranging from ultraviolet (UV) to near-infrared (NIR). In this contribution, we report on the design and characterization of a photonic integrating circuit for the optical addressing of Yb+ ions using a foundry-fabricated single-layer Al2O3 nanophotonic platform.

Deep neural networks have become a cornerstone of modern artificial intelligence applications, yet their decision-making processes often remain opaque. In this publication, the integration of explainable AI (XAI) techniques into the manufacturing processes of the optical and glass-processing industry is explored. The work addresses the correlation between sensor-derived process data and the resulting quality of manufactured components using both classical and deep learning models. The need for transparency and interpretability is highlighted, especially in industrial contexts where human operators must understand and trust the system’s output to make informed decisions. The pro- posed approach allows for proactive identification of influencing error factors, paving the way for optimized process control and quality assurance.

Optical Coherence Tomography (OCT) is a widely used non-invasive imaging technique, particularly in ophthalmology, offering high-resolution cross-sectional images of biological tissues. However, traditional OCT faces limitations in penetration depth and sensitivity, especially in highly scattering tissues. This work explores the integration of orbital angular momentum (OAM) with classical OCT. We demonstrate the generation of high-purity OAM modes in an OCT-compatible setup. The purity of these modes was evaluated through phase retrieval and OAM spectrum decomposition. While the use of a broadband source results in a reduction of mode purity, the dominant component remains the correctly generated OAM mode. Our preliminary results suggest the potential for using OAM as an additional degree of freedom in OCT, with applications for noise filtering and resolution enhancement. Furthermore, this approach could be extended to quantum OCT, where OAM entanglement is naturally integrated into the spontaneous parametric down-conversion (SPDC) process for photon generation.

Coherent Fourier Scatterometry (CFS) enables low-power, high-resolution, non-destructive metrology for nanoscale structures. Recent advancements have extended its applications to improving the measurement of critical dimensions, such as steep-sidewall angles of fabricated nanostructures and the detection and shape determination of defects for semiconductor and power electronics applications. Innovations like beam scanning, multi-beam setups, and synthetic optical holography enhance its speed and sensitivity, making CFS increasingly viable for industrial in-line inspection

This study presents a spectroscopic polarimetric imaging system that integrates single-pixel imaging (SPI) with dual-comb spectroscopic polarimetry (DCSP) to achieve scan-less birefringence mapping. The system simultaneously captures amplitude and phase spectra for two orthogonal polarizations using DCSP, while SPI eliminates the need for mechanical scanning through structured illumination with a spatial light modulator. Experimental validation using a USAF 1951 birefringent test chart demonstrated successful reconstruction of spectral-resolved images of amplitude ratio and phase difference, achieving high contrast and effectively resolving coated patterns.

The material sapphire is becoming increasingly important in many technical applications. Due to its high hardness, however, high-quality and efficient mechanical processing of the material poses major challenges. Investigations into planar machining with resin-bonded diamond tools on a CNC lever machine setup are presented. The achievable removal rates are shown to be highly dependent on the tool grain size and are adjustable by the grinding parameters in certain ranges. Minimal roughness Rq≈0.15 μm is achievable with fine D28 grain.

Carbon quantum dots (CQDs) are fluorescent nanoparticles with distinct physicochemical properties that benefit the biomedical fields. Among the various syntheses of CQDs, pulsed laser-based synthesis in liquids offers high-purity CQDs which are ideal for biomedical use. In this work, we explored the various applications of laser-synthesized CQDs from in vitro bioimaging, and fluorescent probes for glucose sensors to their promising anti-angiogenic performance.

In this study, the effects of the pre-annealing process (400°C–600°C) of lithium niobate (LiNbO₃) crystals on the performance of a multifunctional integrated optical circuit (MIOC) for fiber optic gyro (FOG) were investigated through system-level testing.

This work demonstrates the sensitivity dependence on the chosen cavity length for the sensor Fabry-Perot interferometer (FPI), where the smaller cavity exhibits a higher magnification factor compared to the situation when the cavity length is larger than the reference interferometer.

Integrating grating outcouplers into ion traps offers a promising

approach for efficient optical addressing of trapped ions. However, most

existing implementations utilize only transverse-electric (TE) mode grating

outcouplers, where the emitted light is polarized in the plane of the chip. This

restriction imposes constraints on beam geometry and limits the placement

flexibility of grating couplers within the ion trap architecture. In this work, we

present the characterization of a Si3N4 grating coupler with TE and transversemagnetic (TM) modes. The grating enables efficient outcoupling for both

polarizations, albeit with different emission angles. Integrating TM-mode

grating couplers into ion traps expands polarization control by enabling outof-plane polarization, allowing for more flexible waveguide routing and grating

placement, and thereby relaxing constraints on beam geometry design. This

polarization demultiplexing also allows for new functionality by allowing

interacting with the same ion using different polarizations by shuttling it

between beam spots.

Non-uniformly and totally polarized (NUTP) beams have been proved to be useful in polarimetry, because they make faster and more accurate the determination of the Mueller matrix of sample. To simplify the measurement apparatus, it is also desirable that the transverse polarization pattern of such beams remain unchanged during propagation in the free space through an optical system. Beams with such behavior can be obtained, for example, by superposition of suitable higher-order Gaussian modes. In this work, we present some results about the use of NUTP beams with propagation invariant polarization pattern in the determination of the optical parameters of a chiral medium, which exhibit circular birefringence and circular dichroism. In particular, the use of full-Poincaré beams, i.e., beams that present all polarization states across their transverse section, will be studied in more detail.

The development of reliable and precise temperature sensors is crucial in many fields. In this paper, luminescent powders based on yttrium aluminum garnet crystallites doped with praseodymium ions are analyzed for their application as temperature sensors. The emission spectra and luminescence lifetimes in a wide temperature range from 10 K to 1000 K will be presented in this study. In addition, multiphase samples containing YAG, YAM and YAP will be analyzed in terms of the effect of phase ratio on optical properties. The predominance of the YAG phase provides high emission intensity, which extends the operating range of the temperature sensor. However, the presence of the YAM phase results in longer fluorescence decay times because it is characterized by a weaker electron-phonon interaction, which may improve the temperature detection. The YAP phase introduces a red shift of spectral lines, which can extend the sensor's operating temperature range. Changes in the position of the emission bands and the luminescence efficiency will allow the sensor to be adapted to various applications. The research results will enable the development of a precise optical temperature sensor that will be able to operate in a wide range of operating conditions

This work presents a rectangular large core area (R-LCA) PCF with a cladding diameter of 125 μm, a pitch of 9 μm, and a hole diameter of 8 μm. The guided modes were obtained through numerical simulations using COMSOL Multiphysics. This R-LCA-PCF has the potential to be used for refractive index sensing.

In this paper, we present a preliminary three-dimensional numerical investigation to identify the optimal configuration for a metasurface structure specifically tailored for minimization of reflection and the improvement of light intensity transmission in a silicon layer for the visible and near-infrared domains. We employed the finite difference in time and space method to analyse various types of metals and geometries for the meta-atoms that comprise the metasurface. The results demonstrate that the presence of the meta-atoms structures coated with a silica thin film minimizes the reflections with almost 30%.

Metasurfaces have emerged as a promising solution, with the potential to enhance the sensitivity of various biomedical spectral sensing technologies through the utilization of the intense interactions between light and matter at the nanoscale. This work presents the investigation of the potential of a low-cost metasurface platform, comprising nanoaggregates with random configurations, for enhancing fluorescence intensity. The investigation encompasses the fluorescence behaviour of low quantum yields fluorophores such as Nile Red, Rose Bengal, and Crystal Violet (CV) dispersed in ethanol solutions and coated onto the metallic nanoparticle arrays. The highest fluorescent enhancement factor was obtained for CV on silver metasurfaces.

3D photonic band gap crystals can be used to manipulate light, for example to increase the emission of an emitter. An inverse woodpile photonic band gap crystal has been fabricated in silicon by FIB lithography and reactive ion etching. The resulting photonic crystal was then infiltrated with quantum dots in toluene which emit above the photonic band gap. Quantum dots inside the photonic crystal emit with 24 times more intensity than quantum dots outside the crystal and also exhibit a 7 times increase in emission speed.

We describe the theory of optical wavefront shaping, where waves are focused to a predefined focal point deep inside a disordered three-dimensional (3D) opaque medium (e.g., tissue, paint, foam) by shaping the wavefield sent by N external array elements. Our work is motivated by recent studies where wavefront shaping (controlled interference of scattered waves) coexists with classical diffusion for which wave interference appears to be irrelevant. We derive the energy density both near the focus and anywhere in the medium, averaged over realizations after optimization. We find that the average energy density including focusing is described by the C1, C2, C3 and C0 intensity correlations known from mesoscopic transport theory. Remarkably, the background energy density obeys a diffusion equation wherein C2-correlations create an energy source inside. Thus, a classical property (diffusion) coexists with interference. We discuss several energy density profiles proposed in literature, that are associated with optimized transmission by a slab using wavefront shaping. Our results are relevant for applications where the internal energy density in opaque media is crucial, such as in white-light illumination, projection optics, semiconductor metrology, (bio)sensing, and photovoltaics.

This study allows us to understand both the beam structure and the production of NPs in pulsed laser ablation in liquids (PLAL) by modifying the spatial structure of the Gaussian beam. A cylindrical lens was used to focus a femtosecond pulse laser beam to produce Au NPs, resulting in improved NPs yield compared to those obtained using spherical lenses. This improved yield is achieved by efficiently distributing the energy over the sample due to the structure of the focused beam.

While many research fields are driven to higher levels of performance with photonic integrated circuits, the forward design of these systems faces certain limitations. This paper presents a machine learning based approach to design binary metasurfaces to facilitate beam shaping, angle, and polarization state.

We implement Lumerical FDTD and Non-Dominated Sorting Genetic Algorithm III (NSGA-III) to optimize the topology of the outcoupling structure composed of subwavelength pixels, allowing a higher degree of control over the emitted light field. The generated pattern is shown to maintain the desired beam shape and angle while modulating the right/left circular and linear polarization states, allowing scalability of the design for different wavelengths without large distortion of the field properties and promising low fabrication complexity.

It is generally assumed that 3D photonic band gaps behave as perfect reflectors, which would be striking in view of their complex 3D nanostructures. Therefore, we developed an interferometric optical reflectivity microscope to observe phase-sensitive complex reflectivity and intensity reflectivity of nanophotonic structures. We define a measure of the specularity of a sample, where we ratio the complex reflectivity amplitude to the intensity reflectivity. We experimentally observe that the specularity in the gap of 3D Si woodpile crystals is near unity. Thus, 3D band gap crystals are perfect specular reflectors, and remarkably well outside the gaps.

Nanotip metasurfaces, enabling effective optical modulation of incident lightwave, can be employed as a promising candidate to implement different functions, thus significantly improving the lightwave controllability, validity and system integration. However, the light-field sqeezing in nano-meter, so as to significantly reduce the size and improve the efficiency of photonic devices, still remains limited. In this paper, a strong incident radiation response, following with a highly localized surface resonant lightfield excitation and enhancement was clearly displayed with the proposed planar nanotip metasurface. We demonstrate that the structure-dependent reflection in infrared regime can be effectively modulated, and the minimum value is ~41.0% under an infrared radiation of 4.74 μm due to the excitation of surface plasmons at this featured wavelength. Moreover, the near-field resonance enhancement localized at the apex region of the planar nanotip array was also discovered according to the scattering-type scanning nearfield optical microscopy (SNOM) measurement. The intensity of the near-field electronic field component is demonstrated to reach a maximum value of ~75.4 μV. The proposed typical planar nanotip metasurface can be expected to stimulate potential applications about the highly sensitive imaging photodetectors, thermo-photovoltaic, and thermal emitters.

Photonic crystal (PhC) lasers c support lasing from optical bound states in the continuum (BICs), which are non-radiative modes stabilized by symmetry or topological protection in open systems. These BIC modes enable control over not only the frequency and emission direction but also the topological properties, including polarization and topological charge. By altering the PhC lattice geometry, such as the period and hole diameter, lasing from two non-degenerate BICs with opposite topological charges has been demonstrated. This is observed for both TE and TM modes, where modes like TE-1 and TM+1 can coexist and lase simultaneously without annihilation of their topological charge. These results suggest that BIC-based photonic platforms can provide highly tunable, topologically structured, and polarization-controllable coherent light sources, offering new opportunities for integrated photonic device development.

Optical WaveFront Shaping (WFS) uses the physical feature that whereas light scattering is complex, it is a linear process, thus deterministic. The incident wavefront is controlled to focus light through a scattering sample, by spatially dividing an incoming wavefront and modulating the resulting segments with Spatial Light Modulators (SLMs) or Digital Micromirror Devices (DMDs) paired with a holography system.

The main criterion for such a process is the enhancement of the intensity at the target, defined as the ratio of the optimized intensity at the target, and the average intensity at the target for many realizations of the scattering sample.

We focus on the effect of restricting the degrees of freedom of the phase modulating devices on the optimization performance. By turning off certain segments, which contribute very little to the optimization, it is possible to greatly shorten optimizations without a significant loss in enhancement. By shrinking the active area of segments, issues with holography systems occur, as small segments and phase transitions negatively affect performance.

Our results lead to better choices regarding the areas of interest and limits of such optimizations to improve speed and efficiency, which are relevant for WFS applications.

Conventional optical systems for laser beam expansion, collimation, and reflective path configurations in miniaturized atomic gyroscopes face challenges due to excessive volume and component complexity, limiting further optical integration. To overcome this, we propose a compact optical architecture using an off-axis freeform mirror that integrates beam expansion, collimation, and reflection for vertical-cavity surface-emitting lasers (VCSELs) into a single freeform surface. We fabricated an off-axis freeform reflective mirror and a total internal reflection mirror, both achieving polarization preservation above 98%. This approach offers a promising solution for miniaturizing atomic sensors.

In this work, a motionless method to achieve quantitative phase imaging in single-pixel microscopy based on the transport of intensity equation is presented. In this approach, a digital micromirror device is used to generate wide-field structured illumination over the sample. The light resulted by the interaction between the sequence of light patterns and the sample is collected using a bucket detector. The integration of a focus tunable lens allows the motionless acquisition of multiple intensity images required for applying the transport of intensity equation. Quantitative phase retrieval in active single-pixel microscopy is demonstrated by imaging calibrated pure-phase test targets.

Photonic circuits, engineered to couple optical modes according to a specific map, serve as processors for classical and quantum light. They can be employed for tasks like vector-matrix multiplications, unitary transformations, and nonlinear operations, forming the basis for application like quantum computing. Liquid-crystal meta-surfaces (LCMSs) have recently been employed for optical simulations of quantum walks (QWs), by coupling transverse light modes with the polarization degree of freedom. These can be modeled as patterned waveplates, whose optic-axis orientation angle is non-uniform in space. In general, the system’s size and complexity (number of LCMSs) grow with the simulated evolution, affecting its feasibility in quantum experiments due to optical losses. Based on [3], we present an implementation of a purely quantum photonic circuit for a two-photon quantum walk experiment using a spontaneous parametric down-conversion source with visibility > 95%. We perform up to 5-step walks, involving up to 30 modes.

While indirect optical geometry measurements do not rely on the optical characteristics of the target’s surface, they depend on the presence of the fluorescent particles in the surrounding medium. In order to overcome uncertainty limits due to the random particle distribution, a well-controlled single particle is applied using an optical tweezer. As a result, the surface of a transparent object is detected via a trapped silica particle to pave the way for more precise indirect optical geometry measurements and to make measurable what is difficult to measure with state-of-the-art direct optical principles.

This work discusses the full-field measurement and characterization of guided ultrasonic waves (GUWs) on technical surfaces. The measurement is realized by a lensless digital holography approach with stroboscopic coherent illumination. This approach ultimately yields the height distribution featuring the deformation caused by the GUWs, which is then statistically evaluated using the structure function. As a result, GUWs are captured single-shot and characterized regarding wavelength and amplitude.

We propose a precise method for measuring the rotation angle of the polarization plane using a polarization-holographic grating combined with a quarter-wave plate. This approach enables real-time measurements with high accuracy.

To reduce the computational load for Digital Image Correlation (DIC) measurement, this paper proposes a multi-level grid interpolation and motion characteristics analysis initial guess method. In an image, all subsets that need to be calculated are divided into multiple levels of grids. Based on the deformation parameters of low-level grid cells, the initial deformation parameters of higher-level grid cells can be estimated. In the image sequence of quasi-static material tests, the deformation parameters of the 0-level subsets in the next image can be estimated by analyzing the motion characteristics of those subsets. The proposed method is validated using images from the classic "DIC Challenge". The algorithm proposed in this paper can effectively improve the accuracy of overall initial value estimation, and improving the overall execution speed of the algorithm.

We calculate and analyze the quality factors Q and the intensity and sensor

figures of merit (IFoM and SFoM) evaluating the intensity and sensor coupled with the leakage of modes of the reflection flux and of the plane-wave and locally excited transmitted fluxes of insulator-metal-insulator (IMI) and metal-insulator-metal (MIM) 2D planar thin-film stacks, here glass-Ti-Au-air and glass-Ti-Au-SiO2-Au-air respec-

tively. These thin film stacks sustain a single surface plasmon polariton (SPP)

and multiple planar wave guide (PWG) modes. The Q, IFoM and SFoM of the 3D

dispersion graph (in-plane wave vector kρ/k0 ∈[0, 1.52]/frequency ω ∈[0.5,

2.7] eV/observable) are calculated and analyzed along 2D cuts where either the

in-plane wave vector kρ/k0 or the frequency ω are varied the other independent

variables being kept fixed.

A general and simple semi-analytic theory of multilayer dielectric gratings is presented. It extends a previous work [J. Opt. Soc. Am. A 41, 252 (2024)] that assumes symmetric grating profile and Littrow mounting to gratings of asymmetric profiles in off-Littrow mounting.

The prediction of optical properties dominated by light scattering in particulate media composed of high-concentration and polydisperse particles is greatly important in various optical applications. However, the accuracy and efficiency of light propagation simulations are still limited by the huge computational burden and complex interactions between dense and polydisperse particles. Here, we proposed a new optimization strategy that can effectively and accurately predict optical properties based on Monte Carlo simulation with particle size and dependent scattering corrections. Both the scattering parameters of particles and the experimental reflectance spectrum are fully examined for verification. Furthermore, using the weighted solar reflectance of particulate media as a representative optical property, both numerical simulations and experiments confirm the superiority and universality of the proposed optimization approach in a variety of materials systems. Moreover, our work can guide the design of particulate media with specific optical features insightfully and will be applicable in many fields involving multiparticle scattering.

Precise beam shaping is essential for many trapped-ion quantum computing architectures, where grating couplers are the conventional solution for delivering light from a photonic chip to an ion. The required beam properties, such as a Gaussian profile with a well-controlled beam waist, pure circular polarization, and steered in a specific direction, require a sophisticated design space. We replace standard grating structures with metasurfaces consisting of subwavelength pixels, transforming the problem into a complex inverse design challenge. Here, conventional multi-objective optimization methods require extensive computational resources and must be re-run for each new target parameter. We propose a hybrid deep learning-driven approach to accelerate the design process by integrating a surrogate-assisted optimization pipeline and generative models. Our approach significantly reduces computational cost while improving flexibility in beam engineering, making it a promising candidate for scalable ion-trap integration.

Active tuning of photonic integrated circuits (PICs) in the visible regime is essential for programmable devices, but conventional designs suffer from fixed bandwidth and response times. Here, we demonstrate (i) all-optical and (ii) electro-optical control of extraordinary optical transmission (EOT) to achieve on-demand tunability in PICs. In the all-optical scheme, the EOT signal’s intensity and spectral position are dynamically modulated by tailoring surface plasmon resonance (SPR) dynamics via ultrashort light pulses. Time-resolved 3D FDTD simulations and wavelet transform analysis reveal that tuning excitation wavelength and duration optimizes SPR modes, enhancing EOT efficiency to 95% and improving response times by extending SPR lifetimes to 100 fs. For electro-optical control, we integrate a voltage-tunable quantum emitter (QE) into the EOT structure. The QE’s resonance frequency, adjusted by an external bias, modulates the coupled SPR dynamics. This shifts the EOT signal frequency by up to 181 meV across QE transition wavelengths while enabling continuous intensity modulation with a 10³ depth. Our approach enables real-time reconfigurability and performance optimization of EOT device, addressing critical needs for biosensing, high-resolution imaging, and molecular spectroscopy.

This work models light transmission through metal-dielectric-metal microcavities supporting Coupled Surface Plasmons (CSP). An extended Fabry-Pérot formula reveals two plasmonic resonances that merge beyond a critical cavity thickness. Remarkably, transmittance at these resonances remains high and nearly constant for thicknesses exceeding the light's penetration depth. Results at a 1 μm wavelength show over 10% transmittance up to 3.5 μm, offering new insights for photonic device design

Oligonucleotide optical switches are suitable molecules capable of turning on or modifying their light emission on molecular interaction with well-defined molecular targets. Among all the possible switches, molecular beacons (MBs) represent a powered tool for the detection of RNAs, such as micro-RNA (miRNA), long noncoding RNA (lncRNA), and messenger RNA (mRNA), which play an important role as indicators of the progress of different pathologies in the human body, from the chronic ones to cancer. In this work, the decennial activity carried on by the authors on the design of MBs specific for different targets, on their use as biorecognition elements for different optical setups (i.e. fluorescence o SERS based platforms), on their application for drug delivery in cell, etc., has been reported.

Nanostructures on bodies of biological inhabitants in severe environments can exhibit excellent thermoregulation, which provide inspirations for artificial radiative cooling materials. However, achieving both large-scale manufacturing and flexible form-compatibility to various applications needs remains as a formidable challenge. Here a biomimetic strategy is adopted to design a thermal photonic composite for high-efficiency daytime radiative cooling. Cicadae, thermophilic insects that have been startlingly reported to have higher population densities as the urban heat island (UHI) intensity is growing, have attracted little attention for their thermoregulation. In this work, the optimized thermoregulatory ability of golden cicada’s hair is first studied. Then, a microimprint combined with phase separation method is developed for fabricating a biomimetic photonic material made of porous polymer–ceramic composite profiled in microhumps. The composite demonstrates high solar reflectance (97.6%) and infrared emissivity (95.5%) in atmospheric window, which results in a cooling power of 78 W m-2 and a maximum subambient temperature drop of 6.6 °C at noon. Moreover, the technique facilitates multiform manufacturing of the composites beyond films, as demonstrated by additive printing into general 3D structures. This work offers biomimetic approach for developing high-performance thermal regulation materials and devices.

We utilize the de novo protein design to create bioinspired four-helix bundle maquettes capable of supporting artificial chromophore arrangements. These robust, water-soluble scaffolds were functionalized with Zn-pheophorbide a (ZnPa) and Rhodamine 101 (R101). The resulting complexes exhibited broad visible absorption, and modulated ZnPa emission due to energy transfer from R101 to ZnPa. Spectroscopic analyses supported by Molecular Dynamics simulations revealed the occurrence of excitonic coupling between ZnPa and R101. Our work demonstrates the potential of rationally engineered proteins as a sustainable platform for developing light-harvesting systems.

Photonic structures integrated with responsive photoresists have garnered significant attention, particularly following the advancements in two photon lithography. The pH responsive photonic array presented exhibits robust structural stability and generates progressively changing structural colours in transmission across various pH buffered solutions, highlighting their strong potential for biosensing applications.

Lanthanide β-diketone complexes, renowned for their luminescence, are pivotal in designing multifunctional advanced materials for diverse applications, including lasers, energy harvesting, and sensing. This work utilizes supramolecular Eu³⁺ bis-β-diketones as dopants in poly-methyl-methacrylate (PMMA) to fabricate highly transparent, luminescent polymeric slates. These systems, exhibiting exceptional molar brightness, are explored as luminescent solar concentrators (LSCs) for building-integrated photovoltaics (BIPVs). PMMA/Eu³⁺ slates, synthesized via cast polymerization, demonstrate high transparency (AVT=92%, CRI>98) and effective UV absorption (300-400 nm), crucial for both aesthetic integration and UV protection. Coupling these slates with Si solar cells yielded LSC-PV devices, characterized according to standard guidelines. Notably, these devices achieve comparable performance to literature analogues, despite a 10-100 fold reduction in Eu³⁺ content, demonstrating efficient material utilization.

We report a significant reduction in taper transmission loss by processing ZBLAN fibre under a controlled argon environment. The contrast between tapers processed under argon and ambient air is highlighted through quantitative loss measurement as well as by investigating the surface morphology of the tapers using optical and electron microscopy.

Composite optical fibers with Yb³⁺ doped crystals embedded in glass matrices combine the benefits of crystalline and glassy phases for photonic applications. This work demonstrates the feasibility of preparing composite fibers within glass systems. YbPO₄ crystals were incorporated into silica via solution doping of the soot layer during MCVD, followed by collapse and fiber drawing. Electron and Raman microscopy confirmed the survival of ~100 nm crystals after processing up to 2100 °C. Another fiber was prepared by embedding LiNbO₃:Yb³⁺ crystals in phosphate glass using a direct doping method. Both fibers demonstrate the potential of post-treatment-free, crystal-in-glass fibers for laser applications.

To the best of our knowledge the inscription of tilted fibre Bragg

gratings via the point by point method, without beam shaping, has been demon-

strated for the first time. Using two parallel inscribed FBGs we have been able

to create cladding and core mode coupling effects indicative of a tilted FBG.

A negative curvature hollow-core fiber design with double pole-anchored cladding elements is numerically proposed for spectral filtering. The fiber structure is investigated for improvement in filtering ability through manipulation of the pole length. The findings reveal reduced confinement losses as low as 0.0003 dB/km for filtered and 0.0054 dB/km for unfiltered wavelengths yielding enhanced loss modulation depth.

We demonstrate the first all-fiber mid-infrared ring cavity laser. The laser comprises a single-mode ZBLAN optical fiber coupler, a tapered pump combiner, a polarization controller, and an Er:ZBLAN fiber. The laser is characterized with a pumping wavelength of 0.976 μm, exhibiting continuous wave emission in the wavelength band of 2.8 μm, with maximum output power of 36 mW.

Optical microcavities have emerged as a powerful platform for investigating fundamental aspects of non-relativistic quantum mechanics, owing to recent advances in controlling the transverse state of light in these systems. We recently employed this platform to explore a long-standing question in quantum tunnelling. While quantum tunnelling has been studied since the early days of quantum mechanics, certain aspects—particularly the duration of tunnelling events—remain contentious.

In our experiment, we examine the motion of two-dimensional photons within a system of two coupled waveguide potentials, imprinted as a height profile on one of the cavity mirrors. In this system, the transfer of population between the waveguides serves as a clock, allowing us to measure particle speeds along the waveguide axis.

Applying this technique to exponentially decaying quantum states at a reflective potential step, we establish an energy-speed relationship for tunnelling particles. Our results reveal that lower-energy particles exhibit higher measured speeds within the potential step. These findings contribute to the discourse on tunnelling times and, independently, serve as a test of Bohmian trajectories in quantum mechanics. Regarding the latter, our observed energy-speed relationship is found to be inconsistent with the particle dynamics predicted by the guiding equation in Bohmian mechanics.

Second-order nonlinear optical materials with high refractive index and wide transparency range are of high demand for various photonic applications. Here, we present nanostructures fabricated in wafer-bonded crystalline aluminum indium phosphide (AlInP). The nanostructures exhibit strong enhancement of second-harmonic generation due to higher-order anapole excitations. Our results illustrate the potential of AlInP for nonlinear nanophotonics.

Terahertz technologies offer unique advantages for communication, sensing, and imaging, yet integrated platforms struggle to perform efficiently in this range. Thin-film lithium niobate, a nonlinear photonic platform, enables compact, broadband, and high-speed terahertz sources through efficient frequency conversion. In this talk, I present our progress on developing sub-terahertz continuous-wave sources on lithium niobate chips, aiming to bridge the gap between electronic and photonic systems for next-generation terahertz integration.

We have observed for the first time a parametric down conversion process within a solitonic waveguide. This feature ensures an optimal mode-overlapping between the interacting waves. Moreover, the excited photorefractive nonlinearity enables a phase-locking regime that allows the temporal overlapping of the interacting pulses too. A broadband PDC is then possible within a waveguide without special needs for phase-matching and temporal sinchronisation.

Traditionally, the resolution of optical microscopes is limited to about half the wavelength used. Single-Molecule Localization Microscopy (SMLM) achieves super-resolution by isolating blinking fluorophores across multiple acquisition frames, reaching resolutions down to single nanometers. However, high-density samples present challenges, as overlapping point spread functions (PSFs) limit accurate localization with conventional, e.g. sCMOS, detectors. Single-Photon Avalanche Diode (SPAD) arrays offer new quantum correlation-enhanced techniques to improve detection sensitivity and emitter density resolution in SMLM. Here, we demonstrate a photon-correlation-based approach for multi-emitter fitting and high-density SMLM in a scanning configuration.

A 23-pixel SPAD array with integrated time-correlated photon counting is used as the detector in a fluorescence confocal-scanning microscope. Crucially, fluorophores are single-photon emitters. The photon arrival times are used to compute the second-order quantum correlation of the signal, which is directly related to the number of emitters in the scanning location. This information makes it possible to locate fluorophores with overlapping point spread functions, consequently, SPAD arrays provide the ability to image in high emitter densities, which enables faster data acquisition and dynamic imaging.

Joining the rich photo-physics of organic materials with the exquisite sensitivity of optical resonances to geometry and refractive index enables a plethora of devices with unusual and exciting properties. Examples from my team include flat microcavity sensors for interference-based detection of the mechanical forces exerted by cells, microlasers for real time sensing of cellular activity and long-term cell tracking, as well as the development of implants with extreme form factors that support optical stimulation of thousands of neurons deep in the brain with unprecedented spatial control. Very recently, by driving the interaction between excited states in organic materials and resonances in thin optical cavities into the strong coupling regime, we unlocked new tuning parameters which may enable a new generation of thin film optical filters with angle-independent characteristics as is required for more compact fluorescence-based sensing devices.

This study details the integration of optical fiber-based and electrochemical biosensors within a specially designed microfluidic system. It will present the results of a bioassay using an aptamer specific to tumor necrosis factor alpha (TNF-) on the hybrid opto-electrochemical system.

We demonstrate single-molecule detection of DNA using a low-cost,

miniaturized microscopy platform. Despite significant reductions in size and

cost, our system achieves performance comparable to a research-grade TIRF

microscope, with a limit of detection of 10 pM. Finally, we propose a path

toward wearable single-molecule sensors through integration with photonic cir-

cuits

Optical emitters in two-dimensional (2D) materials are emerging as ultrabright and robust optical probes for fluorescence based sensing of single molecules in physiological conditions. Controlling their spatial and spectral properties, however, remains challenging. Here, we demonstrate that thermally induced wrinkles in exfoliated hexagonal boron nitride (hBN) flakes act as nanoscale channels capable of localizing both optical emitters and biomolecules. Wrinkle formation is governed by the thermal expansion mismatch between hBN and the substrate, generating strain gradients that activate visible-range emitters. We perform structural and optical characterization of the wrinkles using atomic force microscopy (AFM), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy and single-molecule fluorescence imaging. Our results show that hBN wrinkles form optically active nanochannels that can be filled with liquid, and provide nanofluidic confinements suited for single-molecule transport and detection. These represent a promising platform for on-chip optofluidic sensing with single-molecule resolution.

The advancement of Genetically Encoded Voltage Indicators (GEVIs) has enabled real-time monitoring of voltage dynamics at subcellular resolution. Among various GEVI platforms, microbial rhodopsin-based GEVIs are particularly promising due to their superior sensitivity and spatiotemporal resolution. These indicators have the potential to enhance our understanding of complex cellular events such as synaptic transmission and neuronal plasticity. We present a set of nanofabricated tools to aid achievement of this goal. We employ Laser-Assisted 3D-Printed Nanostructured Arrays to guide neuronal development, optimizing network architecture. In parallel, we explore plasmonic enhancement strategies to boost the kinetics and fluorescence brightness of GEVIs. These top dop-down approaches dovetail with bottom-up genetic engineering of GEVI structure to optimize the experimental design for the investigation of subcellular voltage dynamics at various scales.

Superconducting Nanowire Single-Photon Detectors (SNSPDs) are well known for providing a combination of single-photon sensitivity, low jitter, and high efficiency. Their dynamic range is generally limited to detecting one photon per event, causing dynamic range issues. To mitigate this problem,we present time-gated SNSPD detectors. We showcase our work from simple schemes giving switch-off switch-on transition times of about from 100 ns and improving those to the sub-nanosecond range.

Superconducting Nanowire Single-Photon Detectors (SNSPDs) are well known for providing a combination of single-photon sensitivity, low jitter, and high efficiency.

We present our recent developments on fast-recovery and arrays of SNSPDs specifically tailored for optical communication applications. We perform a full characterization of the detectors and we show their performance on a table-top optical communication setup, emulating a deep space optical communication (DSOC) experiment. We measured data rates exceeding several hundred Megabits per second (Mbits) depending on the communication protocol conditions. These results demonstrate the suitability of this technology for optical communications.

The ITER Upper port Wide Angle Viewing System (UWAVS) is designed to use wall and plasma luminance detected by visible and MWIR cameras at high spatial resolution and frame rates to provide information on the divertor wall temperature and related operational parameters. The modular UWAVS optical system is divided into four subsystems: Front-End Optical Module looks directly at the divertor. Following, light traverses the Interspace Optics Tube and the Bio-shield Optical Labyrinth to the Back-End Optics and Cameras in the port cell. Here light is split in four different channels and imaged. Design is defined by environmental conditions and accessibility and has a strong influence in the alignment and tolerance methodology. The in-vessel subsystem must endure extreme environmental conditions, requiring tight manufacturing and alignment tolerances, while module position and tolerances are somewhat more relaxed. Analysis on alignment tolerances sensitivity and STOP (Structural-Thermal-Optical-Performance) was performed for each of the four UWAVS subsystems. Individual module tolerances and STOP analyses were integrated to obtain an evaluation on the full system performance. Results of the simulations suggest it is possible to build a complex optical system to transport light over the required distance of 21 meters in ITER , while maintaining imaging performance.

We introduce a tabletop high harmonic generation scatterometry technique to extract structural and material characteristics of periodic nanostructures. Grazing incidence reflection scatterometry enables fast and robust measurements of linewidth and groove height with 20 nm and 2 nm precision respectively, paving the way for ultrafast spectroscopy on layered heterostructures.

The study of cultural heritage (CH) objects benefits greatly from non-invasive techniques like hyperspectral imaging (HSI), which enables material identification and spatial mapping. Due to the heterogeneous composition of CH artifacts, combining complementary techniques is essential for comprehensive analysis. However, handling such high-dimensional datasets remains a challenge. We present a computational protocol that combines spatial and spectral dimensionality reduction to enable early-stage fusion and efficient analysis of fused data, through multivariate methods, with a focus on Uniform Manifold Approximation and Projection (UMAP). We introduce an open-source plugin for Napari viewer, which allows for UMAP-based exploration of fused multimodal datasets. Our approach is demonstrated in case studies involving reflectance and photoluminescence data fusion, showcasing its effectiveness in detecting degradation phenomena and revealing material complexity in both plastic artifacts and historical paintings.

In line with the energy transition it is desirable to replace fossil fuels in the curing process of industrial powder coating. Infrared curing is an approved method for flat steel strip surfaces in the steel industry. However, powder coatings are often applied to complex geometries with cavities, where shading reduces the efficiency of infrared curing. IR-emitter arrangement in the reflective heating chamber, their geometry and the dwell time of the components are therefore crucial for a successful and efficient process. In addition, process optimization has to consider the optical parameter variation of the powder coating during the procedure to adjust the radiant power for different coatings and components. For that matter, measurements in the NAPUBEST prototype system are compared with optical simulations of the setup to get the simulation parameters in agreement with reality and thus provide a foundation for the design layout of industrial processes. For fast heating, in this investigating we chose short wave emitters.

Femtosecond direct laser writing as a 3D-printing technology has transformed the field of micro-optics. Over the last decade, complexity and surface quality of printed optical components have ever increased from simple micro-lenses⁠ to multi-element systems⁠, printed spectrometers and multimodal OCT-probes. This rapid development reflects the large potential and application range of 3D-printing technology. Especially medical applications, like OCT, fluorescence or endoscopy require small scale optical systems with high fidelity. But similar, industrial metrology or imaging applications can profit from the many degrees of freedom and miniaturization potential of this technology.

However, the almost unlimited design freedom regarding surface shape, microstructures, apertures and geometry has to be controlled during the optical design process under limiting manufacturing and material constraints. Due to the small size of only 10-1000 micron, moreover diffraction effects need to be considered by appropriate wave-optical simulations.

This paper highlights relevant aspects in the design and simulation of 3d-printed systems. It presents multiple design examples, ranging across micro-optical imaging-, illumination- and sensing-systems for various applications.

This contribution presents a method for producing serial junction heterogenous nanowires through three-dimensional(3D) printing of vertically freestanding nanostructures. Serial junction can be implemented by sequential printing of two different materials. One major issue is accurate positioning of the printing nozzle at the end of the pre-fabricated nanostructure for sequential printing of different material. Typically, nozzle-based direct printing method involves an optical microscope for positioning of the nozzle. However, optical microscopy often suffers from difficulties in identifying the position in the depth axis, distinguishing overlapped objects, resolving nanoscale features. In this study, we present a novel positioning method based on visualizing the nozzle tip with scattered light that is sensitive to contact. Direct 3D printing of PEDOT:PSS and P3HT serial junction heterogenous nanowire was demonstrated via precise positioning of the nanocapillary nozzle with the tip scattered light. Our direct printing method provides a simple route for producing heterogeneous junction nanowires in a position-selective manner, which can be used in light-emitting devices, image sensors, and solar cells.

Computer-generated volume holograms (CGVHs) contain 3D refractive index modulations designed to create complex-shaped wave fields for various optical applications. Two-photon polymerization (2PP) lithography is a single-step fabrication method for such CGVHs that allows the tailoring of refractive index distributions by applying locally varying printed powers. In this work, we fabricate 3D Ronchi gratings on top of modified optical fiber using two different printing powers. To expand the beam to illuminate the whole grating structure, we use coreless termination fiber (CTF). This approach paves the way for fabricating complex CGVHs on the fiber tip by tailoring refractive index distributions through controlled power variations.

Where diffraction orders propagate parallel to periodic structures, reflection and transmission spectra exhibit branch points. In the vicinity of these branch points, the spatial Fourier coefficients of the electromagnetic fields must be regarded as multi-valued functions and resonances from different Riemann sheets contribute. The square-root-like singularities at the branch points interact with resonances in a unique way that results in pronounced asymmetric Wood’s anomalies with discontinuous first derivatives. Multi-valued rational approximations can explain the shape of these features and can make the resonances on different Riemann sheets accessible.

Information extracted from a system’s quasi-normal modes—obtained via numerical solvers—should provide a means to reconstruct spectral expansions of photonic response functions (like the $T$-matrix). These spectral representations provide broad-band frequency predictions which should, in principle, even provide efficient time-domain simulations. However, time-domain implementations are typically constrained by the practical requirement of truncating the infinite spectral expansion, which introduces non-physical predictions, particularly at frequencies far from the region of interest. In this work, we show how physical and mathematical bounds on the response functions can be used to systematically adjust the spectral residues, thereby compensating for the effects of truncation.

Adaptive Optics (AO) is a key technology to enhance the imaging performance of ground based astronomical telescopes, compensating the atmospheric aberrations through an adaptive mirror. To enhance the efficiency of these AO systems, many observatories aim to integrate the adaptive mirror within the secondary mirror of the telescope, resulting in an adaptive secondary mirror (ASM).

TNO is developing ASM’s based on a unique and highly efficient electromagnetic actuator technology, which high force output enable the use of relatively thick mirror shells (>3,5mm), and no need for active cooling through their high energy efficiency. These aspects lead to an overall highly robust and reliable ASM system, which is considered a key requirements for such active components that are built into the heart of the telescope.

TNO has realized two prototypes ASM systems for the NASA IRTF telescope (Ø24cm,and 36 actuators, readily installed and tested) and the UH-88 telescope (Ø62cm and 204 actuators, currently going through factory acceptance testing). In this talk the recent results of these ASM’s will be presented. Furthermore, an outlook will be provided on the future developments including the ASM for the KECK telescope (Ø1.4m and ~3400 actuators).

This work discovers two hidden cases of blockwise recurrence in Zernike computations. Based on these findings, a new computation scheme for Zernike polynomials is proposed. It uses one Pascal triangle for all internal factors, thus avoiding calculations of factorials, cos/sin, inverse matrix, etc., and meets the requirements of computatonal accuracy, high speed, low memory footprint, and flexibility.

Mid-Spatial Frequencies (MSFs) are structured surface errors on

optical elements that often require a full wave-optics treatment beyond the limits

of geometrical approximations. Within the context of paraxial scalar wave-optics,

we introduce the Grating Mode Series Expansion (GMSE) method—an

efficient approach for modeling MSF propagation through astigmatic, first-order

optical systems. By decomposing wavefront perturbations into discrete grating

modes on top of an envelope beam, GMSE enables the analytical propagation of

each mode, accurately capturing interference effects and spatial energy redistribution.

The framework is further developed into an algorithm that sequentially

models both form errors as well as MSFs, at arbitrary distances from pupil

planes. From this method, we derive intuitive shift relations that reveal three

key phenomena: (a) MSFs can induce measurable beam shifts at apertures, (b)

even weak MSFs can produce significant non-uniformities in pupil-plane irradiance

due to interference, and (c) the transition between imaging degradation

and stray-light contribution is formalized as a function of system parameters.

The method and its implications are demonstrated through representative case

studies and form the back-bone for the description of MSFs propagation in nonparaxial

systems.

Global optimization in optical design is particularly challenging for aspheric and freeform surfaces due to their complex, non-symmetric nature and the presence of numerous local minima in high-dimensional design spaces. Traditional optimization methods often struggle to efficiently escape these local minima, leading to suboptimal solutions. To address this, we propose the Simple Saddle Point Detection (SSPD) Algorithm, which enhances optimization by systematically identifying transition points that connect different design regions. By leveraging these pathways, the algorithm enables a more structured exploration of the design space, improving the convergence toward high-performance solutions. This study applies the SSPD approach to optimize complex optical systems, including catadioptric and multiple (folded) imaging mirror systems, where conventional methods face significant limitations. The results demonstrate that this approach is highly effective in refining aspheric and freeform optical designs, facilitating more efficient and reliable global optimization. Finally, we present the global search results as a closed network, highlighting the capability of SSPD to navigate complex design landscapes and achieve superior optical performance.

Increasing accuracy requirements for optical systems require taking thermal disturbances into account at an early stage of the design process. Therefore, a simulation method is presented with a mesh-based absorption algorithm, to account for the temperature distribution in a lens. Having this information, e.g., temperature dependent material properties can be used or thermal deformations can be considered.

Light revolutionized our vision of technology. Carrying five internal degrees of freedom, it offers unlimited capabilities in light-matter interactions. The recent advances in coherent light sources enable remarkable progress in harnessing degrees of freedom and boost light-induced applications. The further increasing demand for controlling the light states catalyzes technological innovations in laser-based systems. In this presentation, I will focus on our recent advances in developing laser systems capable of delivering high power optical vortices with exceptionally high modal purity. By employing the coherent beam combining technique in the filled-aperture configuration, we show the power scaling of short pulsed high-dimensional optical vortices up to 100 W and modal purity in the range of 92-97%.

We report on a MidIr source generating bursts of intense pulses with

tunable repetition rates in the GHz range. The wavelength is also adjustable

between 2.88 to 3.03 μm. The system is based on an electro-optic frequency

comb emitting at 1030 nm out of which bursts of ns duration are carved and

amplified to several W leading to significant pulse peak power. This Yb-based

fiber system is then used to pump an optical parametric amplifier seeded by a

tunable CW Er-doped fiber laser. Due to the second-order non-linear process

properties, the temporal and spectral structure of the pump are transferred to the

idler wave leading to a transient optical frequency comb in the MidIr spectral

range.

We report on the development of the first red diode-pumped fs regenerative alexandrite amplifier. For seeding the amplifier, we will utilize our previously developed SESAM modelocked red diode-pumped alexandrite oscillator, which generates sub-100-fs pulse durations with nJ pulse energy. We will then amplify these pulses to achieve a pulse energy of 10 μJ. We achieved a continuous-wave (CW) output power of up to 2.8 W with 8 W of pump power, and watt-level output power with up to 4% output coupling using additional amplifier components inside the cavity. This demonstrates that there is sufficient net gain for regenerative amplification.

Passively modelocked solid-state lasers can exhibit two types of instabilities with very different origins. Near threshold, pulses are prone to the Q-switching instability, where pulse energy shows strong periodic modulation over successive roundtrips. This behaviour disappears as the pump power increases, giving way to the fundamental modelocked state—characterized by a single stable pulse circulating in the cavity. At higher pump levels, this state can become unstable again, leading to the generation of multiple equidistant pulses per roundtrip, forming harmonic modelocking states with 2, 3, …, n pulses. These instabilities critically affect laser performance, especially in systems using slow saturable absorbers, where accurate modelling becomes particularly challenging. Despite their practical relevance, analytical expressions for the boundaries of these instability regimes are scarce. In this work, we derive such expressions from a recently proposed generalization of the Haus master equation, providing a compact framework to describe the onset of both Q-switching (QML) and harmonic modelocking (HML) in passively modelocked solid-state lasers. These results contribute to a deeper understanding of the dynamics involved and offer valuable guidance for experimental design and optimization.

We report the post-compression of 180 fs pulses with 610 μJ pulse

energy to 44 fs using an LG0,3 beam in a compact bulk multi-pass cell. As a

result, the peak power of an Ytterbium laser system is boosted from 2.5 GW to

9.1 GW and the topological charge of the beam is shown to be conserved after

compression.

We study the driven-dissipative dynamics of one-dimensional photonic resonator arrays functioning as broadband quantum amplifiers [1,2]. We first analyze linear resonators with incoherent pumping, complex nearest-neighbor hopping, and dissipation. We identify conditions for a steady-state topological phase with broken time-reversal symmetry, where photonic signals propagating along the array are directionally amplified. Remarkably, this amplification is topologically protected against disorder, broadband, and near quantum-limited, with gain growing exponentially with system size [2].

We then explore the realization of such topological amplification using coupled Kerr-nonlinear resonators driven by a coherent pump with linearly increasing phase [3]. This induces parametric couplings with complex phases inherited from the pump, breaking time-reversal symmetry and enabling topological amplification via four-wave mixing. Exploiting non-linearities, we thus alleviate the need for incoherent pumping or Floquet engineering. We characterize the rich topological phase diagram [4] and the non-linear dynamics of the emergent topological phase transition [5]. Finally, we propose a microwave implementation using Josephson junction arrays, predicting high directional amplification performance with current technology [3].

[1] Porras et al. PRL 122, 143901 (2019).

[2] Ramos et al. PRA 103, 033513 (2021).

[3] Ramos et al. arXiv:2207.13728 (2024).

[4] Gómez-León et al. Quantum 7, 1016 (2023).

[5] Rassaert et al. arXiv:2411.08965 (2024).

TBA

\abstract{Quantum correlations, particularly squeezing and entanglement, are essential in quantum technologies such as metrology, computation, and simulation, as well as in foundational studies. In quantum optics, these phenomena are often intertwined: two squeezed beams can be transformed into entangled beams by mixing them at a beam splitter, and vice versa. However, it is less common to encounter states where two beams are simultaneously squeezed individually while retaining global entanglement. These hybrid states evidently present potential possibilities for applications. In this work, we propose a compact single-cavity source based on a nondegenerate optical parametric oscillator operated below threshold, capable of generating such light—signal and idler beams that are quadrature-squeezed individually while maintaining global entanglement. This behavior arises from an additional linear coupling between the signal and idler, resembling a beam-splitter interaction. We discuss two physical implementations of this system: one based on intra-cavity electro-optic modulators and the other on optomechanical interactions. This unique combination of local and non-local quantum correlations opens the door to novel quantum communication and metrology protocols.}

We performed an experimental and numerical study of an Indium Phosphide photonic integrated circuit designed for quantum random number generation. We investigated the dynamics of two weakly mutually coupled semiconductor lasers and the transient evolution towards the synchronization of the lasers’ optical phases. The simulated dynamics with the experimentally adjusted parameters were found to be in qualitatively good agreement with the experimental time traces. The results provide a better understanding of the evolution towards synchronization and a foundation for the optimization of the photonic quantum random number generation system.