Conference Agenda

Nonlinear photonic systems are a promising platform for photonic reservoir computing due to their high bandwidth, parallelism and low power consumption. These devices can potentially enhance or, in some scenarios, replace CMOS-based electronic computing systems. However, a significant challenge lies in the limited scalability of photonic technologies that rely on one-to-one implementations of artificial neurons or logic gates. In this presentation, we will present our research on complexity-driven neuromorphic photonic systems, where complex nonlinear interactions among thousands of optical waves within single optical components drive information processing. Specifically, we will discuss how the nonlinear interactions between optical waves, crucial for efficient photonic reservoir computing, can be adjusted and controlled in gain systems such as integrated lasers or doped fibres. This fine-tuning aims to optimise the system's performance and identify an optimal "complexity" threshold for learning.

In the framework of optical frequency conversion, metasurfaces have elevated the potential for effective interfacial nonlinear coefficients through various modes of field localization. For the generation of pulsed ultrafast terahertz (THz) signals, metasurfaces present a viable alternative in the domain of surface-scalable sources driven by low-power oscillators (using nJ pulses). However, recent innovations have predominantly relied on surface plasmons (metals) and, more broadly, on excitations within non-transparency windows—conditions that typically impose limitations on applications and the choice of platforms. Here, we demonstrate the utilization of a fully-dielectric, fully transparent semiconductor that exploits surface-nano-structure-mediated resonances alongside its inherent quadratic nonlinear response. Our system exhibits a remarkable 40-fold efficiency enhancement in comparison to the non-decorated substrate.

We theoretically demonstrate the generation of clean few-cycle pulses in a three-stage all-bulk multipass cell scheme. By meticulously selecting the number of round trips and the width of the material used in each cell, we are able to keep the three stages in the enhanced frequency chirp regime. The results show the generation of short and clean pulses, with compression factors approaching 50 with a final duration below 1.5 cycles.

Whispering-gallery-modes resonators (WGMR) are effective switching devices when either coated or filled with non-linear material. We present examples of all-optical switching of hybrid WGM using polyfluorene, a methacrylate azobenzene and an acrylate derivates. We have studied the Kerr non-linear effect and thermal nonlinearities in a such hybrid systems.

We propose an AlGaAs microring resonator design for the generation of an optical frequency comb by means of the interplay between harmonic generation and Kerr effect. Modal phase matching imposes specific waveguide geometries and, consequently, it impacts the nonlinear efficiency of the system. We show the dynamics of χ(2) + χ(3) comb generation resulting from type-I modal phase matching.

Photonic bound states in the continuum (BICs) have enabled a new class of spectrally selective metasurfaces supporting ultrasharp resonances, enabling breakthroughs in higher-harmonic generation, strong light-matter coupling, biodetection, and lasing. However, many implementations still face constraints related to large metasurface footprints, fabrication limits requiring constant resonator heights throughout the structure, or limited numbers of resonances in a given metasurface area. In this talk, I will present some of our recent concepts for obtaining additional nanophotonic functionalities in BIC-driven systems, including the arrangement of resonators in radial configurations for polarization invariance and reduced footprints, height-driven BICs for obtaining maximally chiral light-matter interactions, and active resonance control by incorporating an electro-optically active polymer. Finally, I will show how BIC metasurfaces with continuously varying structural parameters can be leveraged to spatially encode spectral and molecular coupling information simultaneously, enabling new perspectives for biochemical spectroscopy.

Exceptional points (EPs) attract lots of attention due to the richness of the phenomenology associated to their presence in the complex eigenspectrum of coupled non-Hermitian systems. Here we provide both a coupled mode theory analysis and an experimental investigation of two nanolasers interacting through a channel-mediated coupling. We demonstrate the transition from Parity-Time (PT) symmetric to PT-broken regime using a thermo-optic control over the laser frequency detuning. This regime is associated with a significant reduction of the laser threshold as well as we a enhanced sensitivity to external perturbations in the vicinity of the EP.

Our investigation focused on fluorescence enhancement mechanisms using metal nanoantennas with Alexa Fluor-647. By exploiting numerical modelling tools, we fabricated non-interacting Au nanodisc arrays on glass substrates, achieving a maximum fluorescence enhancement factor of 180 at an optimal spacer thickness of approximately 10 nm. Comparative analysis with bare glass substrates revealed significant improvements in excitation and emission dynamics, attributed to nanoscale field confinement and the Purcell effect. Time- and space-resolved photoluminescence measurements unveiled a distance-dependent interaction between the fluorophore and localized plasmons, modulated by thin polyelectrolyte monolayers, with prevalent radiative processes in samples exhibiting maximum signal.

The manipulation of the the field from quantum emitters directly at the source level is becoming an increasingly viable option for obtaining single photons with specific polarizations or phase profiles. In this context, the combination of metasurfaces with surface propagating modes like Bloch Surface Waves have emerged as an ideal candidate. In this work we present a radially distributed metasurface-like grating designed to produce vortex beams with arbitrary spin and orbital angular momentum. This functionality is realized through its synergy with a dipole-like source, coupled with a TM polarized Bloch Surface Wave.

Two dimensional (2D) semiconductors are exceptional materials for exploring light-matter interactions at the nanoscale. Here I will discuss the integration of monolayer semiconductors and hybrid nanophotonic platforms based on Mie-resonant nanostructures, achieving enhanced light-matter interaction up to the strong coupling regime and generation of strain-induced single photon sources.

High-precision biosensors for single or few molecules detection play a central role in numerous key fields, such as environmental monitoring and healthcare for early-stage disease diagnosis. In the last decade, laser biosensors have been investigated as proofs of concept, and several technologies have been proposed. Here we propose a demonstration of polymeric whispering gallery microlasers as biosensors for detecting proteins at low concentrations. Free space microlasers have the great advantage of working without any need for waveguiding for input excitation or output signal detection. The photonic microsensors can be easily patterned on microscope slides and operate in air and solution. We could detect down to 400 pg of protein without specific binding, and few tens of pg/mL with specific binding.

New photonic techniques need to be developed to improve personalised medicine methods in tissue engineering. In the case of severe bone injuries, difficulties arise when creating platforms where cells required to be efficiently adhered. Femtosecond laser ablation appears as a versatile technique for modifying the surface of materials with high precision and neat outcomes. Thus, a strategy combining 3D printing of biopolymeric scaffolds and femtosecond laser ablation is proposed to design a device with enhanced material properties in terms of cell growth for bone tissue regeneration. Three different patterns were proposed, and it was proven that cell adhesion improvements rely on the pattern profile, assessing that grooved scaffold successfully increased cell adhesion and proliferation in comparison with micropitted samples.

Assessing HER2 expression in breast cancer cells holds significant diagnostic and prognostic importance. Traditional methods like immunohistochemistry and in situ hybridization suffer from low sensitivity and misclassification rates. In this frame, techniques such as vibrational microscopies can ensure, together with low costs and analytical speed, both high accuracy and precision. Herein, we propose a combined Raman and SERS approach for characterizing 4 breast cancer cell lines and normal cells with varying HER2 expression levels. We show that Raman spectroscopy offers a promising alternative, providing unique molecular fingerprints for cell types based on their biochemical signatures. Its non-invasive nature and ability to detect subtle changes in cellular metabolism make it ideal for cancer cell analysis. Coupled with machine learning techniques like PCA and LDA, Raman spectroscopy can classify different breast cancer subcategories accurately. Surface Enhanced Raman Scattering (SERS) further enhances sensitivity, allowing the detection of single molecules like HER2 receptors. Overall, our results enable fast screening of cancer subpopulation in terms of HER2 concentration and macromolecule cell content. Integration of Raman spectroscopy with SERS offers precise identification and opens avenues for personalized therapies

With continuously improving resolution of today’s (super-resolution) microscopes, a major technical limitation of light microscopy based image analysis is linkage error – a visualization error that is measured by the distance between the cellular target to be detected and the fluorescence emitter used for detection. The linkage error of standard labelled antibodies is caused by the size of the antibody and the random distribution of fluorescent emitters on the antibody surface. In this study, we describe a class of staining reagents that effectively reduce the linkage error by more than five-fold when compared to conventional staining techniques. These reagents, called Fluo-N-Fabs, consist of an antigen binding fragment that is selectively conjugated at the N-terminal amino group with fluorescent organic molecules, thereby reducing the distance between the fluorescent emitter and the protein target of the analysis. Fluo-N-Fabs also exhibit the capability to penetrate tissues and highly crowded cell compartments, thus allowing for the efficient detection of cellular epitopes in a wide range of fixed samples. We believe this class of reagents realize an unmet need in cell biological super resolution imaging studies where the precise localization of the target of interest is crucial for the understanding of complex biological phenomena.

The manufacturing rate of laser-chemical machining (LCM) is limited to avoid disruptive boiling bubbles in the process fluid. Adjustments to e.g. the laser beam or the fluid properties can increase the removal rate. However, the existing understanding of the surface removal mechanisms is insufficient to ensure the removal quality under these conditions. Thus, near-process measurements of the surface geometry and the surface temperature are required for an improved process modeling. Due to the complex process environment, no suitable in-process measurement technique for the geometry or surface temperature exists so far. This contribution presents an indirect geometry measurement approach based on scanning confocal fluorescence microscopy that is integrated into the LCM plant. As a result, it is shown that the approx. 200 μm deep micro-geometry of laser-chemically processed surfaces can be indirectly measured in-situ, i.e. inside the LCM system. The realized setup is designed in such a way that in future it will be additionally possible to measure the temperature by means of the fluorescence life-time.

Bioluminescent systems possess remarkable features, such as high quantum yield and no need for an external light source, that render them highly valuable bioanalytical tools for developing portable biosensors for monitoring molecules, cells, and bioactivities with applications spanning from agro-food to clinical fields. Therefore, bioluminescent biosensors have a great potential to support the “One Health” approach, to guarantee health to humans, pets, wildlife and our environment.

Here we report the development of novel bioluminescent biosensors implementing living cells and cell-free systems immobilized on paper and cotton threads and interfaced to a smartphone as light detector. The implementation of artificial intelligence algorithms to smartphone-based bioluminescence detection is also reported. A paper-based toxicity smartphone biosensor was developed providing, thanks to an Android AI mobile app, quantitative and user-friendly information.

The combination of bioluminescence biosensing with microfluidic thread-based analytical devices (μTADs) provided a sustainable low-cost alternative to paper based biosensing, especially to handle very low volumes of samples (less than 5 µl). We report a proof-of-principle application of bio-chemiluminescence biosensing on cotton threads and, to prompt future applications in point-of-care and point-of need settings, we exploited smartphone detection enabling easy detection of the bio-chemiluminescent signal directly on the thread.

This study deploys the application of Fiber Bragg Gratings (FBGs) in physiological pressure monitoring by integrating an elastomeric, biocompatible coating ranging from 300-500μm, designed to improve sensor functionality for in-vivo pressure monitoring applications. FBGs are favored for their sensitivity, immunity to electromagnetic interference, and compact size, making them ideal for embedding within medical devices such as catheters and guidewires. However, their use has been limited by low inherent pressure sensitivity (3.14 pm/MPa) and the impracticality of thicker coatings described in previous studies. Our approach demonstrates that this unique coating not only boosts the pressure sensitivity significantly—surpassing two orders of magnitude (43.10 times)—but also enhances the signal-to-noise ratio of the optical signal. These advancements enable potential applications in high-resolution manometry, gastrointestinal pressure monitoring, intracranial and intracoronary blood pressure measurements, marking a significant step forward in medical diagnostics and monitoring.

We discuss the implementation of Whispering Gallery Modes Microbubble resonators (MBRs) as unique platforms for photoacoustic (PA) detection and photothermal (PT) spectroscopy. In a first experiment, the MBR transducer allowed to detect the PA signal generated by a suspension of gold nanorods (GNRs) within its core, leveraging on the MBR sharp optical spectrum and high sensitivity towards mechanical perturbations. Both static and flow-cytometry configuration were tested, finding that the MBR mechanical modes help detection by decoupling the environmental noise from the PA oscillation. In a second experiment, the MBR transducer allowed to reconstruct the GNRs absorption spectrum through the photothermal (PT) conversion, leveraging on high sensitivity towards temperature variations. We verified the scattering-free nature of the detection by using milk-stained GNRs suspension. We also found that the active locking of the MBR resonance increases the system sensitivity by an order-of-magnitude. These results make MBRs interesting candidates for combined PA and PT characterisation of extremely small samples for medical diagnosis, quality controls in food safety and chemical production processes.

A novel technique for the realization of superimposed long-period gratings with different grating periods, based on the discretization of a continuous sinusoidal refractive index pattern with a step function, is described. The RI variation is induced step-by-step on a photosensitive optical fiber fiber with a 248nm UV laser beam. Two superimposed long-period grating (LPGs) with different grating periods, so coupling the light to two different cladding modes, were realized, and different sensitivity to refractive index and temperature were exploited for the simultaneous detection of both parameters. The proposed device can be used for the compensation of temperature fluctuations in biosensing.

Whispering Gallery Modes (WGM) are optical resonators with promising applications in chemical sensing. Nonetheless, only few examples regarding the detection of small molecules through WGM resonators have been reported in the literature to date. Here, we report on the detection of the anticancer drug Doxorubicin (DXR) using Layer-by-Layer (LbL)-functionalized WGM fluorescent microparticles. In particular, polystyrene sulfonate (PSS) is assembled in combination with the polycation polyallylamine hydrochloride (PAH) on the WGM surface and exploited as the DXR receptor. The PSS-functionalized WGM particles feature a linear change of the WGM resonance wavelength and linewidth when exposed to DXR at concentrations down to 1 μg mL-1, with good selectivity against other anticancer drugs. Remarkably, detection of DXR in interstitial fluid is also successfully demonstrated.

In the realm of astronomical scientific exploration, deployable and scalable approaches in space telescope systems are reshaping our understanding of the universe. Two revolutionary membrane-based space telescope designs, on-axis OASIS (Orbiting Astronomical Satellite for Investigating Stellar Systems) and off-axis SALTUS (Single Aperture Large Telescope for Universe Studies), have been developed as mid/far-infrared telescope concepts featuring an inflatable primary mirror. Through the scalable primary aperture design, these deployable space telescopes leverage an all-encompassing optical architecture that taps into the uncharted potential of extremely large telescope apertures. These visionary mission and optical designs pave the way for the next generation scalable telescopes of unprecedented dimensions and diffraction-limited imaging resolutions.

We present a mesh-based method for optimizing double-sided freeform lenses to control their caustic effects. Unlike traditional single-sided approaches, we optimize both sides of the lens simultaneously, using a bijective correspondence between the two sides to control light refraction paths. Our approach balances image fidelity, geometric compatibility, and physical constraints. Results demonstrate the method's capability to accurately produce intricate light patterns, opening new possibilities in optical applications.

We discuss an inverse method to compute a freeform two-reflector two-target system. The optical path length constitutes an integral component and can be expressed in terms of position coordinates at the first target. The system is expressed in terms of a generating function, closed with energy balance and requires a sophisticated least-squares solver to compute the shapes of the reflectors. In a numerical example, we illustrate the algorithm's capabilities to tackle even the most intricate light distributions.

The use of beam-based technologies to process optical elements with nanoscale precision enables the fabrication of freeform surfaces. In particular, atmospheric pressure plasma jets (APPJs) have desirable properties, e.g., depth precision < 5 nm, low surface roughness and processing at atmospheric conditions. However, the composition of optical glasses and glass ceramics, containing metal oxides, leads to the formation of non-volatile reaction products that remain on the substrate surface. These residues reduce the etching rate and cause severe roughening of the surface. Laser irradiation has already been demonstrated as a promising option for removing the residual layer and the aim of the current work is to integrate it into the APPJ system for simultaneous processing. Therefore, an excimer laser (λ = 248 nm; tPulse = 20 ns) with a maximum pulse frequency of 100 Hz was added to a plasma jet setup and experiments with varying laser fluences as well as laser frequencies were performed on N-BK7 substrates. White light interferometry was used to analyse the samples. The experiments showed an improved etching result with higher removal rates for the combined process at high laser pulse frequency (100 Hz) and fluences in the range of 0.1-0.45 J·cm-2.

The manufacturing of optical components is subject to constant efforts to optimise production processes in order to achieve high surface qualities under the most economical conditions possible. This includes the refinement of existing technologies or development of completely new production technologies. One possible approach is the combination of conventional machining processes for optical components like diamond turning, grinding or polishing with laser-based processes to thermally influence the surface for improved machining or surface properties. For this, knowledge of the thermal interactions of the laser on the component surface is needed, which in turn requires its metrological acquisition. In this work, measurements were carried out using various methods for the controlled heating of glass surfaces by an infrared laser (λ=1070 nm). Among other things, a clear correlation between the samples surface roughness and the laser absorption is found.

In my presentation, I will discuss the innovative prospectives presented by Free Electron Lasers (FELs) for attosecond science. Specifically, it will elucidate how attosecond metrology and spectroscopy can be implemented at seeded FELs by substituting the necessity for synchronization between the attosecond pulse train and the infrared laser pulse with a correlated examination of the single-shot photoelectron spectra.

Ultrashort light pulses can be used to manipulate electronic and optical properties of solids at extreme temporal scales, paving the way to the study of ultrafast electron dynamics. In recent years, attosecond-based spectroscopic techniques have proved to be an instrumental tool in such studies. To this end, we investigated the effects of crystal orientation on ultrafast photoinjection dynamics in germanium using attosecond transient reflectance spectroscopy (ATRS) aided by time-dependent density functional theory (TD-DFT) calculations. Our results show that ATRS is sensitive to subtle changes in the transient reflectance due to crystal orientation, although carrier photoinjection in germanium is qualitatively robust against crystal rotation, displaying similar photoinjection processes and timings at two different crystal angles.

High-order harmonic spectroscopy is a robust method for probing electron dynamics under the influence of a driving field, capturing phenomena as brief as attoseconds. It relies on the extreme non-linear process of high-harmonic generation (HHG), where intense laser pulses are directed at a material, causing it to emit high-energy photons in harmonics of the laser frequency. In this contribution we explore the possibility to generate high-order harmonics from low-dimensional crystalline solids driven under grazing incidence. We demonstrate that, in this unconventional geometry, the electron wavefunction is ejected from the solid and, subsequently, redirected to it to generate harmonics. Most appealingly, we show that the crystal’s periodicity imprinted in the electron’s wavefunction introduces a revival dynamics closely connected with the matter temporal Talbot effect. These Talbot oscillations are ultrafast (< femtosecond) and leave a distinct signature in the high-frequency harmonic spectrum, in the form of structures extending beyond the main spectral cutoff.

We explore via numerical modeling the generation of very short photon wavelengths in hollow core waveguides (HCW) filled with He gas at high pressures. Propagation of femtosecond driving pulses is first solved using a split-step method and tested against other methods. The propagation along the HCW reveals mode beating seen in quasi-periodic oscillations of the field intensity and phase which in turn will determine the single atom response to the field.

We explore both cylindrical and conical HCW in which the guide diameter varies along the propagation direction. This second configuration generates very high harmonic orders in a regime of quasi-phase matching. We found three spectral ranges which show amplification, at 3.5, 7.6, and 11-13 nm, which are of great interest given their practical applications in spectroscopy, XUV metrology and photolithography.

Ultrafast charge transfer processes in organic materials which occur in organic materials are fundamental for advancing solar energy conversion technologies. Understanding these phenomena on a short time scale induced by visible and ultraviolet (UV) light is crucial for future control and engineering of these molecules. Here, we present a novel attosecond beamline featuring Resonant Dispersive Wave emission for generating sub-3 fs tunable pump pulses in the UV region and High Harmonic Generation (HHG) in a semi-infinite gas cell for isolated attosecond pulse generation in the Extreme ultraviolet range.

In modern optical engineering, tunable optical devices play a crucial role in dynamically controlling key optical parameters, enhancing functionality and adaptability. Various mechanisms, such as electrical gating, optical pumping, mechanical actuation, phase transitions, magneto-optical effects, and nanostructured nonlinearities, enable real-time adjustments at the nanoscale level. This facilitates enhanced functionalities like tunable focusing, beam steering, frequency tuning, and polarization control, along with improved imaging and aberration correction in optical systems. A novel approach involves selectively controlling spatial regions for optical tuning, achieved through organic mixed ion-electron conductors like PEDOT:PSS. This conductive polymer offers flexibility, thermal stability, and easy fabrication, with remarkable electrostatic tunability by injecting mobile ionic species from an adjacent electrolyte. By adjusting the bias between electrodes connected to the polymer, full control over material properties can be achieved, enabling the realization of a tunable broadband gradient index material without complex fabrication processes.

Nanosphere lithography is a cost- and time-efficient tool for the fabrication of various nanostructured materials. Multiple steps of metal layer deposition at different oblique angles were shown to produce complex asymmetric and chiral shapes. Here, we investigate samples in which polystyrene nanospheres are covered by Ag or combination of Ag and Au at a single step (under 45°). In this way, we obtain metasurfaces with asymmetric shells, with a nanohole array formed due to the shadowing effect. We investigate chiro-optical properties of four samples by exciting them in the 700-1000 nm range, at angles of incidence from -45° to +45°; we report on dissymmetry in the total extinction between left and right circularly polarized excitation gext, which follows the rules of extrinsic chirality. We then resolve the transmission of Ag metasurface in terms of hyperspectral Stokes parameters, and we connect the S3 parameter with gext. Finally, we characterize nanohole arrays obtained from the same samples when the nanospheres are removed; we further perform electromagnetic simulations to gain insight into the “egg” shaped nanohole.

All-dielectric, sub-micrometric particles obtained through solid state dewetting support Mie resonances together with a high-quality monocrystalline composition. Although the scattering properties of these systems have been qualitatively investigated, a precise study on the impact given by the effective com-plex morphology of a dewetted nanoparticle to the Mie scattering properties is still missing. Here, by us-ing morphological characterization, phase field modelling and light scattering simulation, we provide a realistic modelling of the single scatterer optical properties. Moreover, by means of the Dark-field Scan-ning Optical Microscopy characterizations and numerical simulations of light scattering, we show how the presence of a pedestal enriched with silicon placed under the SiGe-nanoparticle results in a sharp peak at high energy in the total scattering cross-section. Exploiting a tilted illumination to redirect scat-tered light, we can discriminate the spatial localization of the pedestal-induced resonance, extending the practical implementations of dewetted Mie resonators in the field of light scattering directionality and sensing applications.

Multilayered metal-dielectric nanostructures display both strong plasmonic behavior and hyperbolic optical dispersion. The latter is responsible for the appearance of two separated radiative and non-radiative channels in the extinction spectrum of these structures. This unique property can open plenty of opportunities towards the development of multifunctional systems that simultaneously can behave as optimal scatterers and absorbers at different wavelengths, an important feature to achieve multiscale control light-matter interactions in different spectral regions for different types of applications, such as optical computing or detection of thermal radiation. Nevertheless, the temperature dependence of the optical properties of these multilayered systems has never been investigated. In this work, we study how radiative and non-radiative processes in hyperbolic meta-antennas can probe temperature changes of the surrounding medium. We show that, while radiative processes are essentially not affected by a change in the external temperature, the non-radiative ones are strongly affected by a temperature variation. By combining experiments and temperature dependent effective medium theory, we find that this behavior is connected to enhanced damping effects due to electron-phonon scattering. Our study shows that our system can be used as very sensitive thermometers via linear absorption spectroscopy.

Light containing twisted phase structures, i.e. light carrying orbital angular momenta (OAM), when propagating inside ring-core fibers leads to a complex interference dynamics resulting in the fundamental self-imaging phenomenon known as the Talbot effect in the angular domain. We study the effect in the classical and quantum optics domain and show that it can be used to implement higher-order beams splitters. Interestingly, such beam splitting operations become more compact the higher the splitting ratio. In addition, we show that a similar self-imaging effect appears for whispering gallery modes carrying OAM in step-index multi-mode fibers, which enables the application of the angular Talbot effect in off-the-shelf components. Finally, we extend the study of the angular Talbot effect through combing it with its Fourier-analog, i.e. the Talbot effect in orbital angular momentum space. Thereby we implement the generalized angle-orbital-angular-momentum Talbot effect, which enables full control over the angular intensity distribution as well as the OAM spectrum of the light field. Moreover, the complex self-imaging dynamics can be used to sort OAM light fields, in principle, without any crosstalk and, thus, can be seen a promising method for OAM multiplexing schemes.

Advancements in structured ultrafast laser sources have significantly contributed to our understanding of the fundamental dynamics of electronic and spin processes in matter. Notably, the development of ultrafast sources structured in their spin and orbital angular momentum has been pivotal in probing chiral systems and magnetic materials at fundamental temporal and spatial scales. Thanks to the highly nonlinear process of high harmonic generation, structured ultrafast laser pulses have been brought into the extreme ultraviolet/attosecond regimes.

This talk will review significant works from the last decade that have advanced the field of attosecond structured pulses. The discussion will focus on how these pulses can be generated—for example, how to create attosecond vortex pulses—, and how they can provide new insights into our understanding of ultrafast electronic dynamics.

We present a theory of the transverse orbital angular momentum (OAM) of spatiotemporal wave packets that explains the different values of the transverse OAM of spatiotemporal optical vortices (STOVs) provided by several authors as belonging to different canonical STOVs. The theory also rules out inaccurate values contributed by other authors, closing the debate on this issue.

A novel class of structured propagating waves with parabolic rotational symmetry is introduced for the first time. These are described by exact solutions of the Helmholtz nonparaxial wave equation. Being the result of the separability of the Helmholtz equation, the intensity of these wavefields remains invariant while propagating along parabolic trajectories exhibiting apparent acceleration. Whe will show that superposition of the different wavefields created can present parabolic, spherical or even rectilinear propagation.

In this paper, we introduce a secure optical communication protocol that harnesses quantum correlation within entangled photon pairs. A message written by acting on one of the photons can be read exclusively through measurements of the other photon of the pair. In this scheme, a bright, meaningless optical beam hides the message, rendering it inaccessible to potential eavesdroppers. Unlike traditional methods, our approach only affects unauthorized users, fundamentally limiting their access to the communication channel. We demonstrate the effectiveness of our protocol by achieving secure communication through both amplitude and phase modulation, relying on single-photon measurements, as opposed to most approaches which rely on coincidence measurements. We successfully demonstrate the resilience of the data transfer to noise up to 10^5 times greater than the signal, and we employ this technique for the secure transfer of an image.

We develop a framework that computes two-photon spontaneous emission (TPSE) spectra of a quantum emitter near an arbitrarily shaped nanostructure. The model considers the interaction up to the electric quadrupolar order, which is relevant for nanophotonic structures sustaining strongly confined fields that are used to enhance and to tailor spontaneous emission processes. Moreover, we consider interference effects between multipolar two-photon emission channels, for the first time to our knowledge. First, we show for a s → s transition of a hydrogen atom placed under a silver plasmonic nanodisk a substantial enhancement in the photon-pair emission rates by 5 and 11 orders of magnitude for the two-electric dipole (2ED) and two-electric quadrupole (2EQ) transitions, respectively. Then for the same emitter under a plasmonic graphene nanotriangle, we demonstrate a breakdown of the electric dipole approximation in the TPSE process where the interference between the 2ED and 2EQ transitions is important, as it increases the total rate by 63 %. Third, we explore platforms where entangled photons of different energy are emitted in the far-field in different directions. In the end, our framework is a complete tool to design emitters and nanostructures for the TPSE process, leading to a rich assortment of functional nanoantennas.

Non-Hermitian photonics attracted significant attention as a rising field in optics due to the emergence of numerous physical concepts and novel effects. Unlike systems described by a Hermitian Hamiltonian, where hermiticity ensures system closure to the environment and energy conservation, a non-Hermitian system enables the description of open systems and facilitates understanding of how a system can interact with the environment. We propose an innovative approach for simulating non-Hermitian dynamics by realizing a non-unitary photonic quantum walk, based on a light beam propagating in free space and manipulated via step operators acting jointly on its polarization and transverse momentum. We use the latter degrees of freedom to encode the coin and walker systems, respectively. To induce coin-rotation, we utilize a uniform liquid-crystal (LC) plate. An LC dichroic polarization grating is used instead to obtain a coin-dependent non-unitary translation operation on the walker. Through the combination of liquid crystals and dichroic absorbing dyes, we can manipulate both polarization and light amplitude. This development yields a compact and versatile platform that significantly expands the scope of photonic simulations in studying quantum dynamics. It introduces a new dimension for manipulating topological states, potentially enabling the observation of phenomena related to non-Hermitian topological phases.

Photonic circuits that can manipulate light in a unitary and reconfigurable way are promising candidates for optical processing of both classical and quantum information. However, engineering such circuits poses significant challenges in terms of minimizing losses, increasing the number of modes, and achieving multidimensional dynamics.

Here we present a novel photonic circuit based on spin-orbit photonics that, by realizing up to 20 timesteps of a two-dimensional quantum walk, couples a single input mode to hundreds of output modes. Our circuit consists of three liquid crystals metasurfaces that perform periodic and space-dependent polarization transformations on a light beam, effectively coupling circularly polarized spatial modes with different transverse momenta. These modes form the basis of a two-dimensional lattice where the quantum walk takes place.

We demonstrate the versatility and scalability of our circuit by operating it in different regimes and measuring the output modes distributions, which show high similarity with the theoretical predictions (>87%).

Monolayer transition metal dichalcogenides (TMDs) like WS2 exhibit strong exciton resonances in the visible spectral range that govern their optical response. The excitonic light-matter interaction in these 2D quantum materials is inherently strong and highly tunable, which can be leveraged to realize mutable flat optical elements as well as novel spin-valley coupled information carriers.

Here, I will showcase experimental realizations of coherent coupling to hybrid light-matter quasiparticles known as 2D exciton polaritons (2DEPs) in nanopatterned monolayers of WS2, allowing for enhanced and tunable photonic functionality given directly by the geometry of the monolayer itself. Using guided mode resonances in sub-wavelength gratings structured in mm-sized continuous WS2 monolayers, we can realize dynamic control of light scattered coherently off the hybrid light-matter state via electrical and/or thermal tuning. Further utilization of photonic metasurface concepts allows for angle-dependent amplitude switching of grating diffraction orders via perturbative approaches, leading to expected modulation depths exceeding 13dB stemming from an atomically thin optical element. This opens a path to full active control over the complex optical response in tailored atomically thin metasurfaces via exciton resonance tuning.

The study of Dirac plasmon polaritons (DPPs) in two-dimensional materials has raised considerable interest in the last years for the development of tunable optical devices, plasmonic sensors, ultrafast absorbers, modulators, and switches. In particular, topological insulators (TIs) represent an ideal material platform by virtue of the plasmon polaritons sustained by the Dirac carriers in their surface states. However, tracking DPP propagation at terahertz (THz) frequencies, with wavelength much smaller than that of the free-space photons, represents a challenging task. Herein, we trace the propagation of DPPs in TI-based coupled antennas. We show how Bi2Se3 rectangular nano-antennas effectively confine DPPs propagation to one dimension, enhancing their visibility despite intrinsic attenuation. Furthermore, plasmon dispersion and loss properties of coupled antenna resonators, patterned at varying lengths and distances are experimentally determined using holographic near-field nano-imaging at different THz frequencies. Our study evidences modifications on the DPP wavelength along the single nano-antenna ascribable to the cross-talk between neighbouring elements. The results provide insights into DPPs characteristics, paving the way for the design of novel topological devices and metasurfaces by leveraging their directional propagation capabilities.

Van der Waals (vdW) materials are ideal for nanoscale light-matter interactions. Here, we use quasi-bound states in the continuum (qBIC) to achieve high Q factor optical resonances in hBN and TMDC metasurfaces. In hBN metasurfaces, we achieve spectral tuning across the visible spectrum, enhance non-linear optical processes, and coupling of optically active defects. In WS2 metasurfaces, we observe strong anti-crossing between qBIC resonances and excitons, with Rabi splitting up to 116 meV. These results demonstrate the potential of vdW materials combined with qBIC for advanced nanophotonic platforms and room-temperature polaritonic devices.

In this work, we discuss the challenges associated with measuring and interpreting the vibrational properties of nanomaterials at mid- and far-infrared frequencies, where vibrational bands are often broad and overlapping. This issue is compounded by the complex interaction between infrared light and particulate samples, which depends on packing density and particle connectivity. Preliminary results concerning the far-infrared optical properties of Fe 3 O 4 nanoparticles have been obtained using the two most reliable methods (specular reflectance and attenuated total reflectance). These results are compared to one another and to their Raman counterparts. Finally, the influences of particle size and composition on the vibrational spectra are qualitatively discussed.

Optical sensors based on a plasmonic multilayer stack, such as metal-insulator-metal (MIM), have attracted considerable attention over the past decades owing to their high resolution and high performance compared to conventional surface plasmon resonance (CSPR) sensors for bulk sensing (BS) applications. In this paper we show that CSPR is better than MIM sensors for thin film sensing, i.e. when a dielectric sensing layer (SL) is deposited on the outermost metal layer of the structure. We demonstrate that the deposition of a thin film SL on the top of the outermost-layer of an optimized multilayer structure, i.e. MIM, strongly decreases the evanescent electric field and the field enhancement at metal-SL interface and decreases the sensor’s sensitivity for MIM versus CSPR. By considering the theoretical and experimental results we demontrated that CSPR is more suitable than MIM for thin films sensing applications.

Nucleic acids are essential biomolecules for the functioning of cells. In past years, nucleic acids have been assessing their role in prognostics and diagnostics. The progress of nanotechnology has allowed the fabrication of various type of nanostructured biosensors able to detect them with high sensitivity and specificity. Among the available sensing mechanisms, the sensor technology based on Surface-enhanced Raman Spectroscopy (SERS) is frequently preferred for identifying nucleic acids. In these sensors, natural or synthetic oligonucleotide sequences, acting as probes to hybridize the target molecules, are immobilized on a plasmonic sensing platform. In particular, aptamers, short DNA/RNA sequences, are emerging as new recognition elements for their chemical stability and specificity. Here, we focus on the combination of a specific type of aptamer, a molecular aptamer beacon, and nanostructured SERS biosensors for a sensitive detection of nucleic acids.

We report the experimental and theoretical terahertz absorption characteristics of unprocessed crude oils from Kuwait oil wells. Using frequency domain THz spectroscopy technique between the frequencies from 2 – 18 THz (66 – 600 cm-1) and semi-empirical computational chemistry calculation, five (SA121T, SA-151TS, SA108T, SA-120T, SA159T) of the 30 crude oils revealed characteristic absorption peaks. Experimental data showed absorption peaks at 6.0 THz, 7.7 THz, 13 THz, and 16 THz. On the other hand, the calculated spectral bands of 10 nonane molecules were found at around 2.8 THz, 7.7 THz, 10 THz, and 16 THz. Although only two bands were predicted by the calculation, adding alkane molecules of different lengths (pentane to decane) resulted in the formation of new peaks. These preliminary results suggest that there is a mixture of different alkanes present in the investigated samples, a typical characteristic of unprocessed crude oil.

The localized surface plasmon resonance (LSPR) is a phenomenon which consists in a collective oscillation of free electrons in metal nanoparticles (NPs), it is very sensitive to any changing of the optical properties of the surrounding medium, for instance, provoked by the adsorption or desorption of molecules over metal surface. In our work we investigated the LSPR response of silver NPs chemically grafted onto transparent substrates and exposed to increasing quantities of water vapor inside a vacuum chamber. Extinction spectra are obtained by using an “in situ” UV-Vis spectrophotometer as a function of the vapor pressure inside the chamber. We studied the adsorption and desorption mechanism of vapor over plasmonic substrates. The huge sensitivity and the accessible and cost-effective equipment make these effects promising candidates for various sensing applications, including the environmental monitoring

A scattering snapshot hold an enormous potential for cell class and state classification, allowing to avoid costly fluorescence labelling. Beside convolutional neural networks show outstanding image classification performance compared to other state-of-the-art methods, regarding accuracy and speed. Therefore, we combined the two techniques (Light Scattering and Deep Learning) to identify living cells with high precision. Neural Networks show high prediction performance for known classes but struggles when unknown classes need to be identified. In such a scenario no prior knowledge of the unknown cell class can be used for the model training, which inevitably results in a misclassification. To overcome the hurdle, of identifying unknown cell classes, we must first define an in-distribution of known snapshots to afterwards detect out of distribution snapshots as unknowns. Ones, such a new cell class is identified, we can retrain our cell classifier with the obtained knowledge, so we dynamically update the cell class database. We applied this measurement approach to scattering pattern snapshots of different classes of living cells. Our outcome shows a precise cell classification, which can be applied to a wide range of single cell classification approaches.

Optical Coherence Tomography (OCT) stands out for its ability to combine the high resolution of

microscopy with the penetration-depth of clinical imaging. However, in practice this is still limited to a few

millimetres. Interestingly, the imaging-depth of the latest swept-source systems is not limited by their spectral

width but by the analog-to-digital sampling rate. In lieu of slow reference arm length adjustments, we leverage

opto-electronic frequency shifting. This allows for depth adjustments on the microsecond timescale and a modest

detector bandwidth of 200 MHz . The opto-electronic scheme immediately gives us access to an 8 mm range,

a fourfold increase over the nominal 2 mm range of the source. Moreover, by circumventing the need for a

mechanical reference arm, changes in the axial displacement of the sample can be compensated in real-time.

This makes it attractive for imaging arbitrarily-curved surfaces. We showcase this with wide-field OCT imaging

of the curved retina.

Autofluorescence spectroscopy has emerged in recent years as a powerful tool to report label-free contrast between normal and diseased tissues. In particular, Fluorescence Lifetime Imaging Microscopy (FLIM) has shown detailed profiles of tissue autofluorescence, enabling more informed and rapid tissue characterization, with the potential for translation from the research labs to bedside. We report here the test of our autofluorescence lifetime imaging probe device on four different clinical cases. More in detail, we examined four biopsies, one from a hepatocellular carcinoma (HCC), another from an intrahepatic cholangiocarcinoma (ICC), one from a gastrointestinal stromal tumor (GIST) and the last one from pancreatic ductal adenocarcinoma (PDCA). The results suggest that our autofluorescence lifetime imaging probe, together with phasor analysis, can offer a real-time tool to observe spectral and lifetime contrast on fresh tissues and, thus, is a suitable candidate for improving in situ tissue diagnostics during surgery.

Current surgical resections for Head and Neck Cancers aim for clear margins to prevent local recurrence. However, up to 20% of cases result in positive margins, with secondary surgery increasing the chances of death after 5 years. We envision a MMF endoscope that collects high resolution images using wavefront shaping to scan a 405 nm beam at the fiber tip and collecting fluorescence intensity and lifetime to map tumor margins and detect residual malignant cells. To address the question whether the information contained in the fluorescence and morphology can be used to classify cancer and normal tissues, we used images acquired with a microscope and artificial neural network. Initial findings show promise to separate cancer from normal tissue when training neural networks on FLIM data. Spatial and temporal resolution and required field of view for effective margin assessment are determined.

In this study, we introduce a novel optical setup tailored for measuring scattering spectra of small biological aggregates with minimal sample volumes. Calibration was achieved using Polystyrene beads (PS beads) based on Mie scattering principles, enabling accurate measurements of scattering intensities. Bovine serum albumin (BSA) served as a model for studying protein aggregation due to its predictable aggregation behaviour at elevated temperatures. Analysis of non-aggregated and aggregated BSA solutions revealed significant differences in particle size, underscoring the setup's capability to detect variations in aggregation states. Key findings demonstrate the system's efficacy in monitoring protein aggregation processes, which is critical for biochemical and pharmaceutical research. The precise calibration method and the use of BSA as a validation tool highlight the setup's sensitivity and accuracy in quantifying changes in particle concentration and size due to aggregation. This study provides a framework for analysing protein aggregation and offers insights into the aggregation's impact on scattering properties.

In this study, we report the results of two non-invasive optical methods, Raman microscopy (RM) and polarization-sensitive digital holographic imaging (PSDHI), for distinguishing prostate cancer cells from healthy ones. RM reveals cancer cells metabolize glucose faster, storing it as fatty acids and cholesteryl esters in lipid droplets (LDs). On the other hand, PSDHI shows significant morphological changes in LDs in glucose-incubated cancer cells, including number, volume, and refractive index. High birefringence in cancer LDs under perpendicular polarizations was observed, enabling fast discrimination with over 90% accuracy. PSDHI results align closely with Raman microscopy, suggesting its potential as a promising, high-speed technique for cancer screening purposes.

Venous thromboembolism (VTE) is a common and serious disease which encompasses deep vein thrombosis (DVT) and pulmonary embolism (PE). DVT is created when a blood clot forms in the deep veins of the leg and when the clot migrates through the bloodstream, to lung arteries, it creates a PE. VTE is the third cardiovascular cause of death overall and is responsible for 30000 annual deaths in Europe. After biological and clinical investigation, nearly half of VTE cases have no known origin (idiopathic VTE). Among the patients developing idiopathic VTE, about 30% of them would have a recurrent thromboembolic event, 70% would not be subjected to any recurrence. A balance must be struck between the risks of recurrent thrombosis if anticoagulant treatment is stopped versus the risks of bleeding associated with continued anticoagulation therapy that can go up to the course of decades. The search for new biomarkers allowing to best stear the treatment of patients is thus of major interest. Recent studies seem to link clot’s structure to a risk of recurrence. The aim of our work is to develop an innovative optical method, measuring the evolution of the scattering coefficient of a plasma during ex vivo clot formation.

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Mechanical cracks induced during grinding of brittle materials known as subsurface damage (SSD) reduce mechanical and optical properties of optical components. A characterisation of SSD is needed to guarantee a good quality and to optimize individual processes and processing chains. Current research focuses on non-destructive methods such as optical coherence tomography (OCT) to evaluate SSD depth and distribution and to replace currently established, but time-consuming and labour-intensive destructive methods. Yet the imaging of SSD remains challenging, even with high-resolution OCT providing a high sensitivity. The presented work proposes a combined measurement approach of enhanced SSD imaging by using a potassium hydroxide (KOH) wet etching process prior to OCT measurement. An etching process using 30% KOH at 80°C is applied and resulting etching rates are analysed. It is shown by an iterative etching experiment on optical glass SF6 that the KOH etching process enhances OCT signals of SSD under the surface, revealing up to 2.4-times deeper maximum SSD depths using an identical measurement setup.

Nowadays, more and more complex optical elements are used in optical applications, but this can lead to high costs, a time-consuming manufacturing process and limited availability of unconventional elements. Therefore, in this work, we propose LCD 3D printing as alternative cost-effective technique, which is not only user-friendly but also free from design constrains and enables the fabrication of free-form optics. The tested polymeric materials showed promising results for printed optics and optical applications. In addition, 3D printed optical elements were evaluated in terms of their suitability in selected applications with opto-chemical sensors and imaging techniques, with results comparable to those obtained with the corresponding glass optical elements.

Light scattering in optical systems is caused by various imperfections such as surface roughness, bulk inhomogeneity, contamination, and ghost light beam paths. Control of these scattering sources is crucial, particularly for high-precision optical components, and involves both measurement and modelling from the design phase through fabrication to system integration. Recent developments at Fraunhofer IOF have led to advanced instruments for characterization of both optical components and system. Moreover Light scattering measurements provide not only analysis capabilities but also critical data for optimizing fabrication processes by identifying scattering contributors. Results and applications of these techniques and tools will be presented, highlighting their impact on optimizing optical system fabrication.

Ion beam machining has a long tradition in the production of classical high-end optical components. Sophisticated telescopic or lithographic optics have long been made possible by deterministic and highly reproducible focused ion beam machining on various materials of optical technologies. In contrast to long-lasting production, today's industrial and research applications in the fields of precision optics and semiconductors demand the same or higher qualities, but also higher quantities and productivities. New process approaches have to be found and descriptions for higher material removal without compromising quality have to be created. The authors discuss how productivity can be implemented in ion beam machining.

In recent years, optical nanofibres have become a promising platform for trapping, manipulating and controlling atomic systems. In this work, I will highlight our recent work on the demonstration of multiphoton processes using optical nanofibres embedded in a Rb MOT for the generation of entangled photons and the excitation of Rydberg atoms for all-fibred quantum networks.

We show that step-index multimode optical fibres retain memory of the radius at which they were illuminated, despite the output looking like a seemingly random speckle pattern. We characterize this radial memory effect, and discuss its application to spatial multiplexing for data transmission.

Optical nanofibers (ONFs) are highly suitable candidates for studying Brillouin scattering, thanks to their sub-optical and sub-acoustic wavelengths dimensions. The strong confinement of photons and acoustic phonons enhances the interaction and gives rise to several Brillouin backscattering spectra. In this work, we provide an experimental method based on pump/probe interaction in the radiofrequency domain to measure the Brillouin gain at different acoustic resonances.

We present measurements of the temperature of optical microfibers self-heated by a cw laser emitting at 1.48 µm. The experimental method we have implemented is simple and enables to perform for the first time to our knowledge spatially distributed measurements along the tapers and the microfiber part. Temperature rise of more than 20 °C is measured for moderate powers (200 mW) and relatively large radii (1.45 µm). The results are confronted to a numerical model we have developed and enable to determine range of values for the couple thermal transfer coefficient/surface absorption coefficient.

Optical fibers are of great technological importance due to their well-known unique features. Metasurfaces (MSs) are inhomegeneous 2D array of optical resonators, able to impress to the impinging beam an arbitrary modulation in amplitude, phase, polarization or frequency. Their integration on the tip of an optical fiber is able to enormously expand the fiber functionalities, by endowing a simple optical fiber with extraordinary capabilities of light manipulation. MSs are able to replace traditional bulky optical components, with the great advantage of reducing the size of the devices, thus representing a key element in a multitude of applications in modern optics, including fiber communications, analog computing, optical trapping, sensing, and imaging. In this work we exploit the paradigm of the metasurfaces based on partial-phase control in order to realize OFMT for two main applications: beam splitting and light focusing. In particular, we realized several OFMT featuring beam splitting at different angles and almost equal power on the two beams, and a focusing single-mode OFMT able to efficiently focus light at few microns from the fiber end facet, without the need of a beam expander. We show the design procedure, the fabrication process and the experimental characterization of the devices.

The influence of rapid thermal annealing (RTA) onto chalcogenide Ge-Sb-Se thin films is reported, focusing on changes in optical properties. These materials possess broad mid-infrared transparency covering the most critical absorption bands for (bio)chemical sensing and high third-order optical nonlinearities for potential applications in nonlinear photonics. The parameters of the RTA process within this study include the annealing temperature, heating rate, and the two sample processing methods – one by placing the sample inside the graphite susceptor and the other by simply laying the sample onto the silicon wafer. Selenide thin films were found to undergo a shift of the absorption edge upon the RTA, resulting in an optical bandgap energy increase (bleaching effect) and a notable refractive index decrease. As a result of structural relaxation, such changes show a great potential of RTA in fine-tuning of optical performance of chalcogenide thin films and planar chalcogenide waveguides. The authors acknowledge the IBAIA (101092723) Horizon Europe project, the ANR AQUAE (ANR-21-CE04-0011-04) project of the French National Research Agency (ANR), and project No. 22-05179S of the Czech Science Foundation (GAČR) for financial support.

Random laser (RL) based on Rhodamine 6G (Rh6G) doped silica xerogel, fabricated by a conventional sol-gel (SG) synthesis, was observed around 590 nm, in a large band typical from dye RLs. Different from other previous works, where the xerogel is just impregnated or infiltrated of dye solution, here the Rh6G was added during the SG synthesis. The obtained material was grinded using a mortar and a pestle, and the resulting powder was carefully packed in a sample holder and pumped at 532 nm using a 6 ns pulsed laser. We used spectral and images measurements to perform statistical analysis and describe experimentally the Parisi replica breaking symmetry (RSB) phenomenon in a complex system. These results show that RSB obtained from images is a promising method for RL characterization. Indeed, by calculating the RSB maps, we demonstrate that the RL emission is not a homogenous process, depending on the scattering and gain properties of different regions.

In the last few years, quantized nanolaminates (QNL) have become increasingly popular as a metamaterial in the development for optical coatings. Experiments were often performed using IBS or ALD coating techniques, which yield excellent accuracy but are very time consuming to coat. By using a magnetron sputter system with rotating substrate table, we are able to produce these layers at very high deposition rates and to use these nanolaminates as standalone high index material in optical designs. Due to the properties of QNL to increase the band energy and thus shift the absorption edge into lower wavelength ranges, it is possible to create designs in the UV range that would not be possible with simple Ta2O5-SiO2 material combination in regular designs. In this work we show a selection of different designs such as anti-reflective coatings, mirrors and short pass filters at wavelengths from 266-355nm which covers an important range in laser applications.

Two-dimensional transition metal dichalcogenides (2D TMDCs) have gained significant attention from the scientific community due to their exceptional properties, making them extremely attractive for optoelectronic and photonic applications. However, many exfoliation or synthesis techniques yield 2D crystals with limited crystalline quality and/or small lateral size. Here, we report a facile Au-assisted exfoliation method, yielding high-quality, large-area monolayers with lateral sizes of hundreds of micrometers. A self-assembled monolayer of (3-aminopropyl)triethoxysilane (APTES) is employed to improve the adhesion between the 2D material and the target substrate, dramatically improving the yield and reliability of the exfoliation process. The monolayer nature of the final sample is then assessed by means of Imaging Spectroscopic Ellipsometry (iSE), which enables a quick and reliable thickness mapping over millimeter-sized areas

Vector light beams feature a spatially varying optical polarisation and can exhibit localised structures reminiscent of the skyrmions familiar from the study of magnetic media. We present a theory and experimental measurements of such skyrmions in both paraxial and non-paraxial optics. A key feature for our analysis is the skyrmion field which determines the properties of the skyrmions and traces out field lines. In paraxial optics these field lines are lines of constant polarisation, but in non-paraxial optics, the fact the polarisation ellipses are no longer restricted to the transverse plane, makes it necessary to introduce several different skyrmion fields, each representing a different aspect of the three-dimensional optical polarisation.

The fabrication of Diffractive Optical Elements (DOEs) involves the analog patterning of material surfaces on the scale of light wavelength. This typically requires multi-step lithographic processes. Differently from the photoresists of standard lithography, thin films of amorphous azobenzene-containing polymers (azopolymers) can directly produce a structured surface using a single irradiation step with structured light. The resulting surface reliefs can be used directly as planar phase-modulating DOEs without the need for any post-exposure process. Additionally, the surface geometry and its optical functionality can be reconfigured at will. Here, we demonstrate reprogrammable and ready-to-use azopolymer diffractive gratings, lenses, and holographic projectors, produced by grayscale digital holographic patterns. By exploiting the all-optical scheme based of computer-generated holography, the diffraction behavior of the DOEs is optimized during the developing of structured surfaces. Full all-optical reconfigurability of the fabricated devices is also achieved. Our approach provides a versatile, efficient, and all-optical reversible fabrication framework for DOEs, making it a promising option to overcome the demanding, cumbersome, and irreversible fabrication processes typically involved in the realization of planar diffractive optical devices.

Polarization structured heralded single photons have been generated through spontaneous parametric down-conversion in a type-I dual crystal pumped by an inhomogeneously polarized beam in a general Poincaré mode, i.e. an inseparable superposition of two orthogonally polarized states through two orthogonal orbital angular momentum modes. The polarization structure of the signal photons can be controlled by manipulating the polarization state of their idler photon sisters with zero orbital angular. Due to the separate conservations of spin and orbital angular momenta in a type-I dual crystal SPDC process, any projection of the idler polarization state turns into a unitary transformation of the polarization basis of the signal photons, while preserving the orbital angular momentum modes originally included in the pump. We demonstrate, in this way, the ability to toggle between direct and basis-switched pump-single photon transfer by selectively projecting the polarization of the heralding photon before detection.

A method for the generation of structured laser beams (SLB) and hollow structured laser beams (HSLB) whose transverse profiles are invariant and can propagate to infinity is described. SLBs are formed after passing through an optical system that generates a special waveform as a combination of rotationally symmetric optical aberrations. Transverse profile consists of concentric circles with a very bright central core and a bounding outer-ring. The divergence of the central core 0.01 millirad has been experimentally confirmed. When the system was illuminated with a special vector beam, a hollow SLB (HSLB) beam was generated. Its central part is very narrow and completely dark. Unlike conventional hollow beams, where the electric field strength is zero in the dark areas, an electromagnetic field with the zero Poynting vector is present in this part of the beam. By varying the illumination parameters of the vector beam, it is possible to obtain situations where there is a longitudinal component of the electric field or/and magnetic field in the central core. The simulation results are in good agreement with the SLB profile measurements using a polarization camera.

We analyze polarization diffractive elements with the Fourier transform Jones (FTJ) matrix integrated with the beam coherence-polarization (BCP) matrix. Analytical derivations and experimental results are presented of the intensity, state and degree of polarization and coherence properties of the diffracted field generated by a simple diffractive element consisting in double polarizer rectangular aperture.