Conference Agenda

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.