Conference Agenda

Our work centers on the question how you can use far field diffraction of light to read out or reconstruct sub-nanometer spatial information as relevant for, e.g., metrology in nanofabrication processes, given that you are at the same time free to design a nanophotonic scattering target, free to program the incident wavefront, and able to angle-resolve diffraction patterns over a high NA. We use resonant multiple scattering motifs borrowed from the field of dielectric and Fano-resonant metasurfaces, which provide strong scattering resonances with both strong near fields and characteristic far fields. I will discuss both linear scattering experiments, and experiments in which we measure third harmonic generation diffraction pattterns. The experiments elucidate how metasurface resonances and their interferences optimally transduce tiny near-field perturbations into far field information.

In optical metrology, Fisher information is a central metric that

quantifies the precision that can be achieved in a measurement. For coherent

light, it has been shown that the Fisher information can be written as a Hermi-

tian operator using the scattering matrix of the system. The maximum eigen-

states of this operator are the incident light fields that give the largest possible

Fisher information and therefore give the most precise measurements. Here,

we extend the operator to multiple parameters, representing Fisher information

as a matrix. The measurement precision is related to the inverse of this matrix

by the Cramér-Rao bound, however optimizing the inverse matrix is not trivial.

We consider several scalar functions of this matrix in order to optimize for all

parameters simultaneously, and then corroborate our findings using a scattering

system comprised of coupled dipoles in 2D.

Many researchers consider AI too unreliable for scientific use, but with Simulation Based Inference (SBI) we present a class of ML models that produce comprehensible results that adhere to the high statistical standards of conventional publications. In SBI, the model is trained on simulated samples, which allows the scientist to exert full control over the learned features and only requires to usually much simpler forward measuring process. After the training, the model is used to solve the inverse problem of finding the best parameters given an experimental data point with its variance purely based on the relations defined in the simulator. We present a novel model architecture for the application in nanoimaging and investigate the performance of the method for practical metrology applications.

Artificial neural networks (ANNs) have emerged as powerful tools for imaging through complex scattering media, where conventional approaches fail due to dynamic and unpredictable light propagation. However, the fundamental limits of such ANN-based imaging systems remain largely unexplored. We present a model-free approach to estimate the Cramér-Rao bound (CRB), which sets the ultimate precision limit for parameter estimation, and apply it to evaluate the accuracy of the ANNs trained for imaging through complex scattering media. We compare how well various ANN architectures can localize a reflective target obscured by dynamic scattering. Our approach addresses high-dimensional, non-Gaussian, and correlated data using principal and independent component analysis combined with non-parametric density estimation. Comparing several ANN architectures, we find that convolutional networks with coordinate-aware layers can approach the CRB, achieving near-optimal localization performance. This method provides a general benchmarking tool to assess and guide the design of deep-learning-based imaging systems and opens an opportunity for precision metrology in complex and disordered environments.

In this work, we experimentally demonstrate new types of hybrid supercell metasurfaces that exploit different types of supercells and unit cells in the same design, creating a smooth transition between them. We use this new method to control the phase and amplitude of light at the same time while designing speckle-free holograms.

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.

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

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.

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.

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.