Conference Agenda

Authors: Carlos Álvarez-Ocampo, Juan Julián-Barriel, Anna I. Garrigues-Navarro, Aleksander S. Paterno, Martina Delgado-Pinar, Antonio Díez, Jose Luis Cruz, Miguel V. Andrés

In the classical polarimetric solutions, the light polarization states generator (PSG) and analyzer (PSA) are placed on opposite sides of the medium. Such a solution is difficult to realized and even impossible for some media. An interesting alternative are configurations in which light passes through the PSG, the test medium and, after reflecting off the mirror, comes back again through the medium and the same module (PSG) acting as a PSA. This arrangement can be named one-way double pass Mueller polarimeter. Crucial to the system capabilities is the single module PSG/PSA design. This work verifies the possibility of using in them twisted nematic liquid crystals (TNLCs). There are noticeable differences in the quality of the polarimeter depending on the used components (linear polarizer with a single TNLC, two TNLCs or a combination of TNLCs with a liquid crystal variable retarder). Based on the measurement results, numerical models were created and optimized by minimizing condition number to find the best set of PSG/PSA configurations. The one-way double pass polarimetric systems were then tested in the laboratory. The results show that the use of TNLCs overcomes some measurement limitations and increases the system stability, compared to other solutions proposed in the literature.

This study explores the early detection of degradation in plastic-based cultural heritage objects using non-invasive spectroscopic techniques. The results on artificially aged ABS specimens revealed degradation markers at low exposure levels. Changes in polymer composition were then correlated with mechanical stiffening and increased friction. The approach offers valuable tools for in situ monitoring and preventive conservation of modern art and design objects.

The production of optical free-form surfaces requires a high level of precision and surface quality. The process chain presented combines pre-grinding, fine grinding and ultra-fine grinding using a 5-axis CNC machine in order to achieve high shape accuracy and surface quality. The presented process chain makes it possible to produce free-form surfaces with high geometric precision and optical qualities.

In recent years, non-Hermitian photonics has emerged as a prominent field, exploring open systems with complex eigenvalues. We propose simulating non-Hermitian dynamics via non-unitary photonic quantum walks, leveraging liquid-crystal technology for manipulating polarization and light amplitude.

While mankind has successfully mapped the surface of Mars and landed a rover on a comet (ESA’s Rosetta mission), we still struggle to land a helicopter in a snowstorm, or to explore the seabed with optical means. This contrast reveals a major scientific limitation: our inability to control light propagation in dynamic scattering environments such as fog, turbid water or dense aerosols.

In this talk, I first delineate the operational domain of ultrafast wavefront shaping — the regime where ballistic filtering becomes insufficient, yet enough coherent flux remains to allow real-time correction. I then show that this regime, long considered inaccessible, can now be addressed with existing technologies. Specifically, I demonstrate that current modulators, detectors and control architectures are capable of tackling the fundamental constraints of coherence time and photon-per-mode budget. This opens a new window for imaging and focusing through rapidly evolving complex environments.

In the geometric optics approximation typical of far fields (vanishing wavelength), wavefronts emerge as constant eikonal surfaces.

The electric (E) and magnetic (H) field vectors are mutually perpendicular and tangent to the wavefront. They follow planar elliptical trajectories that reach their elliptical vertices simultaneously, "in phase".

Near a dipole, scatterer, or edge, however, the vanishing wavelength assumption fails.

Here, E and H behave differently.

They still follow planar elliptical trajectories, albeit with different phases, eccentricities, and planes.

We define (i) "vertex time" as the position dependent time when E or H reach their respective ellipse vertex,

and (ii) "phasefronts" as surfaces of constant electric or magnetic vertex time.

The spatial gradients of the vertex time are perpendicular to the E and H phasefronts, defining separate E and H phase velocity vector fields.

As we move into the far field, the E and H phasefronts converge to each other and to the wavefront, providing a quantitative measure of how much the local disturbance deviates from "far field".

Applying this concept to the field of a monochromatic point dipole, we find that, contrary to common assumptions, the dipole has no far field near its axis, no matter how far away.

Metasurfaces enable precise light manipulation, like fostering reflections close to unity, through resonance mechanisms. While traditional Bragg mirrors enable very high reflectivity they limit the achievable thermal noise. Meta-material-mirrors (MMM) can overcome the noise limitations but suffer from limited reflectivity. This trade-off is crucial for next-generation cryogenic gravitational wave detectors, such as the Einstein Telescope, which need high reflectivity and low thermal noise test mass coatings to achieve dramatic sensitivity. Hence, we are proposing a new combined design unifying the advantages from both approaches - composed of an MMM, a Fabry–Pérot spacer, and a Bragg mirror – achieving extremely high reflectance and low thermal noise. We are evaluating different 1D and 2D design approaches to achieve MMM robust to fabrication tolerances while offering broad, high reflection at 1550 nm. A key focus is on bandwidth, manufacturability, and thermal noise. This systematic analysis provides a pathway to promising MMM for production via e.g. character projection electron beam lithography, paving the way for high-performance mirrors in gravitational wave astronomy and beyond.

Metallic nano-objects play crucial roles in diverse fields, including biomedical imaging, nanomedicine, spectroscopy, and photocatalysis. Nano-objects smaller than 15 nm exhibit extremely low scattering cross-sections, posing a significant challenge for optical detection. An approach to enhance optical detection is to exploit nonlinearity of strong coupling regime, especially for elastic scattering, which is universal to all objects. However, there is still no observation of the strong coupling of elastic light scattering from nano-objects. Here, we demonstrate the strong coupling of elastic light scattering in self-assembled plasmonic nanocavities formed between a gold nanoprobe and a gold film. We employ this technique to detect individual objects with diameters down to 1.8 nm. The resonant mode of the nano-object in the nanocavity environment strongly couples with the nanocavity mode, revealing anti-crossing scattering modes under dark-field spectroscopy. The experimental result agrees with numerical calculations, which we use to extend this technique to other metals. Furthermore, our results show that scattering cross-section ratio of the nano-object scales with the electric field to fourth power, similar to surface-enhanced Raman spectroscopy. This work establishes a new possibility of elastic strong coupling and demonstrates its applicability for observing small, non-fluorescent, Raman inactive sub-15 nm objects, complementary to existing microscopes.

Phonon Polaritonic resonances, which arise from the coherent oscillations of atoms or molecules within materials, play a pivotal role in understanding and designing advanced materials with unique optical properties. In hexagonal boron nitride (hBN), these resonances are particularly prominent within the Reststrahlen bands—a frequency range where the material exhibits strong optical phonon modes. One of the most fascinating phenomena within these bands is the existence of Bound States in the Continuum (BICs). These states, despite lying within the continuum of radiative modes, remain perfectly confined without radiating energy, a property that has garnered significant interest for its potential in nanophotonic applications. Our investigation in the lower restrahlen band (LRB) of hBN ranges from 755 cm-1 to 814 cm-1 and focuses on deeply subwavelength polaritonic resonators. We exploit the fact that the polaritons in the LRB are strictly out of the plane, and therefore the fundamental radiative mode of the structure will be z-polarized and give the high-quality factored topologically protected BICs.

In this presentation, I will review the latest developments on the use of AI in optical engineering. We'll see how AI can be used for teaching optical engineering, in particular using AI generative tools. Over the last few years, several uses of AI in optics have been published but few developments have really changed the life of an optical engineer. We'll also take a closer look at how generative AI could be used by optical designers. Finally, we'll look to the future and how we want to build the future of optical engineering with these new tools.

The design of off-axis augmented reality display systems based on freeform holographic optical elements (HOE) is presented. The complex freeform HOE is fabricated using freeform optics. Joint optimization method of imaging and recording systems is proposed considering the imaging performance, diffraction efficiency and design constraints. Prototypes including near-eye display and head-up display systems are developed. Larger FOV and more compact structure are realized, compared with the systems using traditional HOEs.

We propose a method to design freeform imaging systems using inverse methods from nonimaging optics. A linear optical map in phase space implies that the ratio of source and target energy distributions is a constant. The performance of the inverse freeform design is compared to a classical design by raytracing parallel beams of light and comparing the corresponding spot sizes. The inverse design significantly outperforms the classical design.

In the present paper we investigate how optimization algorithm can be tailored to improve the lens design process. We replaced gradient-based optimisation methods by the Covariance Matrix Adaptation Evolution Strategy (CMA-ES). This stochastic algorithm is considered more robust and is well suited to avoid local optima often found in optical design. In addition, the algorithm is paired with an augmented Lagrangian method to incorporate constraints handling inside the computation framework. Performances are illustrated on a photographic zoom lens.

We present a fully optical system for the convolution of spatial features in photochromic media. The method relies on imprinting the Fourier transform of a mask into a photochromic sample using 405 nm light, and subsequently performing a convolution using a second, non-activating wavelength (470 nm). Our approach offers reconfigurability and dynamic training capabilities, overcoming the rigidity of traditional optical correlators. Experimental and simulated results demonstrate the system’s ability to distinguish spatial features with high selectivity, enabling compact and efficient optical pattern recognition. This work paves the way for new applications in optical signal processing, machine vision, and embedded neuromorphic photonic hardware.

Photonic Ising machines leverage large-scale parallelism for solving large combinatorial problems, yet multiple minima hamper Metropolis-based algorithm. A double single-pixel detection approach enables adiabatic energetic transitions from nonlocal to local Hamiltonians, finding the ground state of complex landscapes.

I will show experimental results with nonlinear quadratic materials, in particular lithium niobate and barium titanate, for optical computing.

controlling light in complex media by wavefront shaping allows focusing and imaging, but it is also possible to control quantum states, such as indistinguishable photon pairs. I will discuss how one can control such states through a multimode fiber, and how it can be used for various tasks, ranging from emulating simple quasi-unitary circuits, to basic machine learning tasks, with a potential quantum advantage.

Field-resolved detection at near-petahertz frequencies provides exceptional sensitivity, broad bandwidth, and high dynamic range, enabling attosecond temporal and sub-diffraction spatial resolution. In a technique known as Femtosecond Fieldoscopy, ultrashort laser pulses impulsively excite molecular vibrations in resonance with the near-petahertz carrier frequency. This initiates vibrational coherence at the trailing edge of the pulse, which decays exponentially based on the molecular dephasing time.

The transmitted electric field encodes information about the excitation pulse, the sample’s picosecond-scale response, and a prolonged signal from atmospheric gases lasting hundreds of nanoseconds. By detecting this response in the time domain and applying Fourier analysis, the technique yields spectroscopic data with outstanding sensitivity and dynamic range. This performance is achieved by temporally gating the molecular response away from the excitation pulse.

Enabled by recent advancements in ytterbium laser systems, Femtosecond Fieldoscopy has successfully resolved overtone, Raman, and combination bands in liquid samples. Moreover, the method has been advanced for real-time sampling and extended to non-perturbative, label-free imaging.

This talk presents an overview of these recent developments as demonstrated by my group, highlighting the broad potential of this emerging spectroscopic tool.

We combine super-resolution and label-free microscopy by using a donut-shaped pump beam to confine harmonic generation to a sub-diffraction region. This Harmonic Deactivation Microscopy (HADES) can enable (sub-)fs temporal and at least 100-nm spatial resolution.

We present the comprehensive characterization of a series of harmonic fields generated in a ZnO crystal by a few-cycle MIR driving pulse that spans the visible to mid-infrared (MIR) spectral region. The characterization is conducted using the recently developed Plasma-Induced Frequency Resolved Optical Switching (PI-FROSt) technique. We demonstrate the ability of this method to accurately characterize the MIR driving field (λ = 3.2 μm), as well as both odd and even harmonics up to the fifth order. The total spectral bandwidth extends over an exceptionally wide range of 2.6 octaves. All assessments validate the high precision of the field reconstructions and confirm the suitability of the PI-FROSt method for the metrology of over-octave-spanning waveforms. The results offer valuable insights into the fundamental mechanisms governing harmonic generation and emphasize the crucial influence of propagation and cascading.

A plethora of recent studies have shown optical modulation of high-harmonics generation in solids, in particular, suppression of high-harmonics generation has been observed by synchronized or delayed multi-pulse sequences. These works illustrate that high-harmonic generation can effectively be used to study the microscopic electron dynamics in solids on the femtosecond timescale. Moreover, the all-optical switching demonstrated has numerous potential applications: These range from super-resolution microscopy to nanoscale-controlled chemistry, and highly tunable nonlinear light sources. Here we demonstrate the use of elliptically polarized light to spatially shape and confine high-harmonic generation from solids. This technique of spatial polarization gating provides a step towards a universal high-harmonic-based all-optical super-resolution imaging technique in solids. We demonstrate the common ellipticity response of high-harmonic generation in solids and show that we can reproduce these results with simulations based on the semiconductor Bloch equations. Proof-of-principle measurements show that with spatial polarization gating we can obtain sharper and smaller emission features than with conventional high-harmonic imaging, enabling higher-resolution imaging. This opens the door to resolving ultra-fast phenomena such as the insulator-to-metal phase transition in strongly correlated materials not only in time but also in space.

Exciton-polaritons are hybrid light–matter quasiparticles that arise from the strong coupling between excitonic resonances and confined optical modes in microcavities. While foundational studies have primarily focused on GaAs-based heterostructures, the emergence of two-dimensional semiconductors—such as transition metal dichalcogenide (TMD) monolayers and layered perovskites—has opened new avenues for exploring polariton physics in novel material and photonic regimes.

This presentation focuses on the simultaneous enhancement of light–matter coupling and polariton nonlinearities by engineering both the electromagnetic environment and the excitonic properties of the active materials. Coupling efficiency and interaction strength are further improved through unconventional cavity designs that leverage phenomena such as surface optical modes and bound states in the continuum, as well as through material innovations like suspended monolayers and single-crystal layered perovskites.

The results establish 2D polariton systems as promising platforms for fundamental investigations in the strong and ultrastrong coupling regimes, as well as for the development of integrated photonic technologies for classical and quantum information processing.

We demonstrate a nonlinear AlGaAs photonic chip generating biphotons with high-dimensional spatial correlations. Photon pairs are generated by parametric down conversion in a waveguide array and simultaneously spread through quantum walks along the various waveguides, allowing to generate various types of high-dimensional entangled states of light. We further implement the Su-Schriefer-Heeger model and demonstrate the topological protection of the SPDC process against disorder. These results highlight nonlinear waveguide arrays as a promising platform for exploring the interplay between nonlinearity, disorder and topology in quantum photonic circuits.

Lithium niobate-on-insulator (LNOI) has emerged as a cornerstone for on-chip nonlinear optics, combining strong second-order nonlinearity with low-loss waveguides and nanofabrication compatibility. We demonstrate compact and efficient optical frequency converters built on a 4-inch LNOI wafer. Using an optimized process—integrating waveguide definition with post-etch domain inversion—we realize second-harmonic generation (SHG) with on-chip efficiency approaching 90%. This performance benefits from quasi-phase matching (QPM), tight optical confinement, and smooth waveguide sidewalls. Compared to traditional chip-scale approaches, our method offers improved manufacturability and consistency without compromising nonlinear efficiency. The devices are well suited for scalable integration in systems for frequency translation, amplification, and quantum light generation.

Bragg Scattering Four-Wave mixing (BS-FWM) is used in fibers to frequency shift single photons. The main limitation of this nonlinear process is the phase-matching requirement. In this work, we investigate how this condition can be controlled by changing the fiber temperature. We then are able to optimize the efficiency of the BS-FWM process for selected wavelengths. This tunability by temperature is beneficial for fiber-based actively multiplexed single photons sources : it is possible to generate photons and shift their frequency with the same fiber and wavelengths involved.

We contrast the self-organization of light in a nonlinear optical cavity against the recently introduced theory of self-organized bistability (SOB). This reveals that the nonlinear optical cavity may serve as a platform for the first experimental realization of SOB and drives further research into information processing in nonlinear optical cavities.

to be announced

Filter-based spectral systems are highly competitive due to their compactness, simplicity, and well-defined spectral characteristics. However, their primary drawback remains low detection efficiency. This work explores various strategies to enhance detection efficiency. While an additional row of beamsplitters can significantly improve illumination, alternative folded beam path designs—eliminating the need for beamsplitters—prove to be far more effective. Additionally, a novel approach utilizing a freeform mirror is introduced, enabling differential adjustment of detection efficiency across different spectral regions. For the first time, a comprehensive comparison of these strategies is presented.

Exposure of the human skin to sunlight is essential for Vitamin D production. Due to our modern indoor lifestyle an increasing part of the population shows insufficient Vitamin D levels, especially in wintertime. Exposure to artificial UVB radiation can help in maintaining a sufficient Vitamin D level. The provided dose should be high enough to be effective, but low enough not to cause damage to skin or eyes. We designed a UVB module for integration in office luminaires that provides a very low UVB irradiance level that leads to an effective dose in a full working day. Ideally, the intensity distribution for a ceiling-mounted UVB module provides a uniform irradiance level on the face and hands of a sitting person. The final design is a balance between UVB LED availability, optical material use, manufacturing considerations, and required light distribution.

Urban Heat Islands (UHIs), aggravated by intense urbanisation and heat-retaining materials from buildings and roads, affect the thermal comfort of human beings. To mitigate this issue, this study aims to study the thermal performance of cement mortars with coaxial polymeric fibres produced by wet spinning and containing polyethylene glycol (PEG 600 and 1000) (CM_PCF) as phase change material. Samples were irradiated with a solar simulation lamp and monitored through infrared imaging and a thermometer. The CM_PCFs showed surface temperature reductions of up to 1°C. The results suggest that the phase change fibres can increase energy efficiency and support sustainable strategies for mitigating UHIS.

Laser-induced printing is an affordable, fast, and non-contact method for creating high-resolution images. Using plasmonic nanocomposite thin films, it enables the printing of color images with visual effects. However, the color gamut of these images is limited compared to inkjet printing. Therefore, it is necessary to optimize this gamut in order to print images that contain the widest range of colors and are closest to the original. There is currently no model to directly infer the color from the laser parameters used. Instead, a lookup table is required to associate these parameters with actual colors. Since colors vary depending on the type of sample used, it is essential to have a reliable method to quickly determine the laser parameters that produce the best colors. Two methods have been implemented to optimize the color gamut: a genetic algorithm approach to find colors that both increase both hue diversity and saturation, and a Bayesian approach to increase the size of the color gamut. Gamut mapping is then used to print the image, and the quality of the final printed image is assessed using metrics obtained from a psychophysical study.

2D-Transition Metal Dichalcogenides (2D-TMDs) are promising two-dimensional semiconductors with high optical absorption coefficient in the visible range. While exfoliated TMD flakes offer superior optoelectronic performance, scalable large-area growth is essential for real-world applications [1,2]. For light conversion at extreme thicknesses, nanophotonics-based flat optics strategies are key.

We demonstrate that periodic modulation of MoS₂ on nanostructured surfaces—via laser interference lithography—can steer light using Rayleigh Anomalies, enhancing in-plane electromagnetic confinement and broadband photon absorption [3,4,5].

Addressing scalability, we also present cm²-scale flat-optics periodic nanogratings using vertically stacked WS₂-MoS₂ van der Waals heterostructures with type-II band alignment [6]. These engineered vdW structures support scalable applications in nanophotonics, energy harvesting, and photoconversion [7].

This work was supported by the NEST – Network 4 Energy Sustainable Transition – PNRR partnership.

References

1. M.C. Giordano et al. Adv. Mater. Interfaces, 10 (5), 2201408, 2023.

2. C. Mennucci et al. Adv. Opt. Mater. 9 (2), 2001408, 2021.

3. M. Bhatnagar et al., Nanoscale, 12, 24385, 2020.

4. M. Bhatnagar et al. ACS Appl. Mater. Interf., 13, 11, 13508, 2021

5. G. Ferrando et al. Nanoscale 15,4, 1953, 2023

6. M. Gardella et al. Small, 2400943, 2025

7. M. Gardella et al. RSC Appl. Interfaces, 1, 1001-1011, 2024

An array of closely spaced dipole-dipole coupled quantum emitters exhibits collective energy shifts as well as super- and sub-radiance with characteristic tailorable spatial radiation patterns. We identify a sub-wavelength sized ring of exactly 9 identical dipoles with an identical absorbing atom at the center as the most efficient configuration to deposit incoming photon energy to the center.

For very tight dimension below a tenth of a wavelength, a full quantum master equation description exhibits a larger enhancement than predicted from a classical coupled dipole model. Adding gain to such systems allows to design minimalistic light sources with tailorable properties. Examples are mirrorless lasers, non-classical light sources for single or entangled pair photon generation

Such ring shaped structures could be the basis of a new generation of highly efficient and selective nano antennas for single photon detectors of microwaves, infrared or optical frequencies their unexpected properties could be an important piece towards understanding the efficiency of natural light harvesting molecules.

More complex structures of dipole rings are also predicted for robust and low loss long range transport on the single excitation level.

Refs: Optica Quantum 2 (2), 57-63 & Applied Physics Letters 119.2 (2021).

Rare earth (RE) emitters are key materials for efficient light generation due to their chemical and thermal stability combined with high photoluminescence quantum yield (PLQY). Herein, we show that the integration of RE nanocrystals or nanophosphors into designed optical environments allows fine control over the properties of the emitted light without changing their chemical composition or compromising their efficiency. In particular, we theoretically and experimentally study the influence of the optical environment on the radiative decay rate of RE transitions in luminescent nanoparticles forming a thin film, and provide a way to rationally tune the spontaneous decay rate and hence the PLQY in an ensemble of luminescent nanoparticles. Then, we demonstrate a versatile and scalable method to fabricate periodically corrugated nanophosphor surface patterns that exhibit strongly polarized and directional visible light emission. A combination of inkjet printing and soft lithography techniques is used to obtain arbitrarily shaped light-emitting motifs. Such pre-designed luminescent patterns, in which the polarization and angular characteristics of the emitted light are determined and finely tuned by the surface relief, can be used as anti-counterfeiting labels, as these two specific optical features provide additional means to identify any unauthorized or counterfeit copy of the protected item.

Phosphor-converted micro-LEDs (pc micro-LEDs) are envisioned as next-generation high-brightness self-emissive display pixels for near-eye applications such as AR/VR glasses and smartwatches. However, these application settings impose stringent constraints on pixel density, emission efficiency, and angular control, necessitating advanced nanophotonic design strategies. In this work, we first present PyRAMIDS, a computational toolbox for efficient optical modelling in stratified media. Using this tool, we design spacer geometries within the LED stack to promote waveguiding characteristics in the phosphor layer. Experimentally, by integrating periodic corrugations to extract the guided emission, we demonstrate up to a threefold enhancement in pixel brightness compared to conventional LED architectures, validating the efficacy of our proposed approach. Finally, we implement an inverse design-based genetic algorithm to realize compact, aperiodic metasurfaces for emission pattern control, compatible with pixel densities exceeding 10,000 PPI displays - an essential requirement for seamless visual experiences in future smart glasses.

We present a complete framework of stochastic thermodynamics for a single-mode linear optical cavity driven on resonance. The significance of our results is two-fold. On one hand, our work positions optical cavities as a unique platform for fundamental studies of stochastic thermodynamics. On the other hand, our work paves the way for improving the energy efficiency and information processing capabilities of laser-driven optical resonators using a thermodynamics based prescription.

Probing single-protein dynamics at the molecular level is crucial for understanding conformational changes and functional mechanisms. Surface-enhanced Raman spectroscopy (SERS) offers a promising label-free approach to study protein. However, traditional SERS substrates face challenges due to the large size of proteins that are too large to fit in conventional hotspots. Here, we demonstrate that coupled plasmonic nanocavities enhance the Raman scattering up to 10^8 in an unconfined area. We harness the enhanced fields to reveal the dynamics of a single protein by observing time-dependent changes in the Raman spectrum, which is a unique probe of the secondary structure of the protein. We study the effect of the pH and the surface charge of the substrate on the conformation of a single protein of bovine serum albumin (BSA). The dominant secondary structure of BSA is α-helix at pH 7, while at pH 3 and 10, more β sheet and random structure are observed. We use principal component analysis to classify the proteins on the basis of their secondary structure. This work establishes a new possibility of studying large biomolecules and proteins crucial for biomedical applications and understanding the biological functions of proteins and the origin of diseases.

We consider the inverse problem from nonimaging optics: given a source and its light distribution, find the optical surfaces that transform

the light into a desired target distribution. We present models for optical systems with a parallel or point source. The surfaces (lens or reflector) are freeform. Our models are based on Hamilton's characteristic functions and energy conservation.

Phase elements can enhance the performance of imaging systems while reducing their size, by adding continuous phase gradients on top of the geometrical surface. Compared to their typical implementation as diffractive elements, Fresnel optics can achieve similar performance, while maintaining broadband functionality. This work introduces a methodology to optimize such Fresnel surfaces, resulting in high-performance, compact imaging designs.

We present an inverse method to compute freeform reflector and lens surfaces for generalized zero-étendue sources. The initial position and direction of a light ray is parameterized by two source planes and the final position and direction of a light ray is parameterized by two target planes. We use energy conservation to determine optical mappings, and we use the optical path length to derive equations for the optical surfaces. In two numerical examples, we illustrate the algorithm's capabilities to tackle complex light distributions.

Phase space ray tracing is an alternative to (Quasi-)Monte Carlo ray tracing in 2D. We introduce a 3D phase space algorithm and apply it to the compound parabolic concentrator. Our results show that phase space ray tracing outperforms Quasi-Monte Carlo ray tracing in 3D.

We present a hybrid method for reflector design with finite light sources, combining a neural-network-based solver with a deconvolution-inspired iterative correction scheme. Our approach addresses the limitations of classical techniques, which often assume idealized point or parallel sources, by solving a simplified problem using a neural network and refining the solution via feedback from ray-traced simulations of the full finite-source system. We demonstrate the effectiveness of our method on a representative example, showing improved convergence toward a prescribed far-field intensity distribution compared to the approximate problem's solution.

Light-based in-vivo brain imaging relies on light transport through highly scattering tissues over long distances. As scattering gradually reduces imaging contrast and resolution, visualising structures at greater depths becomes challenging, even when using multi-photon techniques. To overcome this limitation, minimally invasive endo-microscopy techniques have been developed that typically use graded-index rod lenses. A recently proposed alternative involves the exploitation of holographic control of light transport through multimode optical fibres [1], which promises superior imaging performance with less traumatic application [2]. Following the review of the fundamental and technological bases, the talk will introduce a 110µm thin laser-scanning endo-microscope, which enables volumetric imaging of the entire depth of the mouse brain in vivo [3]. The system is equipped with multi-wavelength detection and three-dimensional random-access options, and it has a lateral resolution of less than 1µm. Various modes of its application will be presented including the observations of fluorescently labelled neurons, their processes, and blood vessels. Finally, the use of the instrument for monitoring calcium signalling and measurements of blood flow in individual vessels at high speeds will be discussed.

[1] Nature communications 3.1, 1027 (2012).

[2] Light-Science & Applications 7, 92 (2018).

[3] Nature Communications, 14, 1897 (2023).

Optical sensors are limited to measuring intensity. For this reason, wavefront sensors need to convert phase information into intensity modulations. One method to achieve this involves using a Hartmann mask positioned near a camera sensor. This technique is compatible with low-coherence illumination and has been implemented using various encoding optical elements, such as arrays of holes or microlens arrays. For instance, high-resolution and quantitative phase imaging has been demonstrated using a diffraction grating, a method known as lateral shearing interferometry (LSI).

In this presentation, we will illustrate how LSI can also measure broadband speckle wavefields generated through multiple scattering media, enabling digital fluorescence phase conjugation through tissues. Additionally, we will present a generalization of LSI using a birefringent diffraction grating to perform polarimetric LSI of vector beams, which is relevant for optical metrology and polarization-resolved fluorescence microscopy. Finally, we will demonstrate that this generalized principle can be applied to single-shot hyperspectral wavefront sensing, leveraging the spectral dispersion of thin scattering media, with applications in the metrology of ultrashort lasers.

Optical fields’ polarimetry follows well-known principles in paraxial conditions where light polarization is manipulated in transverse planes. In non-paraxial optics such as microscopy imaging, complex media propagation or nanophotonics, it is however still a challenge that requires formalisms appropriate to 3D polarized fields. In this work, we present a few illustrations of how the analysis and control of polarized wavefronts in high numerical aperture microscopy provides access to 3D field’s properties at the nanoscale. We show that the point spread functions (PSFs) of dipole’s radiation through a microscope can be treated similarly to radiation sources possessing 3D-Stokes extensions to 2D paraxial Stokes parameters. By engineering phase and polarization through the detection path of a microscope, it is possible to encode, in a PSF, quantitative information on the 3D orientation of fluorescent single molecules, together with the knowledge of their averaged angular fluctuations (wobbling) and their 3D spatial localization at 10’s nm precision. We demonstrate an extension of PSF engineering to 3D nano-polarimetry to monitor polarization states in 3D (including spin and depolarization), scattered from metal nanoparticles. We finally show the advantages of general 3D Stokes decompositions to analyze polarization properties of light sources through an imaging system.

Plasma mirrors driven at kHz-repetition-rate with waveform-controlled relativistic-intensity near-single-cycle laser pulses produce extreme ultraviolet spectral continua supporting isolated attosecond pulses with diffraction limited beam quality. A newly developed liquid leaf target yields unprecedented stability and duration of operation. This lifts a major obstacle to exploiting plasma mirrors as attosecond pulse sources.

We present studies on boosting high-harmonic generation (HHG) efficiency from solids in the extreme-ultraviolet (XUV) region by two-color non-collinear wave mixing in silica. Our results show that the conversion efficiency of two-color wave mixing exceeds that of single-color HHG by a factor of at least ten. We analyze the underlying mechanisms, revealing that the synergy between Floquet-Bloch dressing and inter- and intraband dynamics under laser irradiation enables efficient carrier excitation, enhancing harmonic yield. Integrating wave mixing into solid-state HHG could help establish compact, coherent XUV sources for applications where traditional gas-HHG is impractical.

Shaping of the spectrum of frequency comb sources is highly beneficial for application that require controllable optical source, such as ranging or communications. However, efficient in-situ reconfiguration of the spectrum is a challenge. We demonstrate spectral shaping of frequency combs in fast-gain active devices by engineering an Aharonov-Bohm phase in a synthetic frequency lattice. By modulating a fast gain circular laser at its resonance and twice this frequency with a relative phase, we created a triangular ladder in the modal space, where the phase added with staggered phase flux. This broke the time-reversal symmetry in the system, allowing for non-trivial gauge fields that manipulate the light. This enable the control over the frequency lattice dynamics, enabling full bandwidth tuning of a strong central lobe in a Quantum Cascade Laser comb. This paves the wave to new efficient and simple reconfigurable optical frequency comb sources.

Light beams exhibit two intrinsic quantized degrees of freedom: spin angular momentum (SAM) and orbital angular momentum (OAM) whose manipulation enables precise control over the topological characteristics of electromagnetic fields. Recently, structured fields formed from a non-separable combination of SAM and OAM have attracted significant interest. These fields correspond to eigenstates of the generalized angular momentum (GAM), an operator merging SAM and OAM components which can yield remarkable fractional eigenvalues. The conservation of GAM, observed through harmonic generation, suggests its potential significance as a fundamental quantum number. In this work, we extend the analysis by examining its conservation laws through second-harmonic generation within an underdense, isotropic, and inhomogeneous plasma; a process governed by dipole-forbidden interaction which implies spin-orbit coupling. Our findings indicate that the symmetry and topological properties of the field are disrupted, leading to conservation of the GAM charge only on average. This symmetry breaking provides an easily detectable signature of the driving field’s topology