Over the past decade, the possibility of manipulating material and chemical properties by using hybrid light-matter states has stimulated considerable interest [1,2]. Such hybrid light-matter states can be generated by strongly coupling the material to the spatially confined electromagnetic field of an optical resonator. Most importantly, this occurs even in the dark because the coupling involves the zero-point electromagnetic fluctuations of the resonator, the vacuum field. After introducing the fundamental concepts, examples of modified properties of strongly coupled systems, such as magnetism, charge and energy transport, and chemical reactivity will be given to illustrate the broad potential of light-matter states.

Meta optical elements product by nanoimprint lithography

Design and application of individualy shaped freeforms arrays

Making an entire Optical Parametric Oscillators (OPO) smaller than a coin

Fermat is a recently founded spin-off by the Brussels Photonics Team (B-PHOT) of the Vrije Universeit Brussel (VUB), Belgium. Based on our proprietary and disruptive ‘First Time Right’ methodology, we develop outstanding imaging optics solutions that are exactly tailored to our customers’ very individual needs.

In this presentation, we will introduce the 'First Time Right' - based ecosystem. Our design methodology is derived from Fermat’s principle and allows calculating all optical surface coefficients that ensure minimal image blurring for each individual order of aberrations. We demonstrate the systematic, deterministic, scalable, and holistic character of our approach ranging from start lens generation to extreme catoptric and catadioptric freeform optical solutions.

Luminescent concentrators are parallelepipeds of luminescent material polished on all sides. The light is confined inside the structure and reaches the edges of the parallelepiped with high power density. The use of LEDs as the pump source provides robustness and cost effectiveness for these new sources that combine power and brightness. The presentation will explain the basic principles of LED pumped luminescent concentrators and describe two types of applications : laser pumping and illumination for imaging.

While acoustic emissions are a method for e. g. the monitoring of bridges or for the assessment of the integrity of tanks, we wanted to investigate them for a further field of application. We tested AEs for the monitoring and assessment of a high-quality finishing process for optical components, the polishing of lenses. This process is - even though - it is of incalculable importance for nearly every optical component still a process which is commonly considered as some kind of black magic. With our research, we want to deliver an insight in this process with interacting mechanical and chemical processes. We want to present a method for the in-situ evaluation of a polishing process.

We use hyperspectral imaging to identify the plastic types constituting mixtures of microplastics directly in water. For the current study we used known microplastics made by milling original pristine plastic sheets and mixed them in water. Using database information and spectral information measured on those pristine plastic we created a decision table enabling the identification. This technique is used under these conditions paving a way towards on-field and in-line measurements.

We report on a stabilized single-frequency Brillouin fiber laser operating at 1.06 µm by means of a passive highly nonlinear fiber ring cavity combined with a phase-locking loop scheme. We show significant linewidth narrowing (below 1-kHz) as well as frequency noise reduction compared to that of the initial pump in our mode-hop free Brillouin fiber laser.

Current 2D windshield head-up displays can lead to driver distractions due to a shift of gaze from the road towards a small area of the windshield. Customizable mixed reality real-time head-up displays can increase safety in transportation due to the holographic road obstacles being aligned with the road scene. Based on accelerated parallel processing algorithms, a 4K spatial light modulator, virtual Gabor lenses and a He-Ne laser, 3D holographic road signs appear within 1.15 seconds in the driver’s gaze on the road.

The study of brain tissue development requires imaging approaches that ideally provide micron resolution, millimeter imaging depth, and multi-contrast capability.

We will discuss recent approaches for large-scale imaging of uncleared tissues, namely color serial two-photon imaging [1] and three-photon (3P) microscopy. We will also present a novel label-free modality that combines some of these concepts, based on third-order sum frequency generation (TSFG). TSFG microscopy provides label-free imaging of red blood cells while being compatible with deep tissue 3P imaging [2].

References:

[1] Abdeladim et al, Nat Commun (2019), https://doi.org/10.1038/s41467-019-09552-9.

[2] Ferrer Ortas et al, Light Sci App (2023), https://doi.org/10.1038/s41377-022-01064-4.

Fast and sensitive detector arrays make Image Scanning Microscopy (ISM) the natural successor of confocal microscopy. Indeed, ISM enables super-resolution at an excellent signal-to-noise ratio. Optimizing photon collection requires large detectors and so more out-of-focus light is collected. Nonetheless, the ISM dataset inherently contains information on the axial position of the fluorescence emitters. We exploit such information to directly invert the corresponding physical model with a maximum-likelihood approach and reassign the signal in the three dimensions, improving the signal-to-background ratio and resolution. We validated our method on synthetic and experimental images; these latter acquired with a custom setup equipped with a single photon avalanche diode array detector. Moreover, our method is compatible with recent developments in ISM data processing and requires minimal knowledge of physical parameters.

Confocal microscopes have been the workhorses of 3-D biological imaging, but they are slow, offer limited depth penetration and collect only ballistic photons. With their inefficient use of excitation photons they expose biological samples to an often intolerably high light burden. The speed limitation and photo-bleaching risk can be somewhat relaxed in a spinning-disk geometry, due to shorter pixel dwell times and rapid re-scans during image capture. Alternatively, light-sheet microscopes rapidly image large volumes of transparent or chemically cleared samples. Finally, with infrared excitation and efficient scattered-light collection, 2-photon microscopy allows deep-tissue imaging, but it remains slow. Here, we describe a new optical scheme that borrows the best from three different worlds: the speed and direct-view from a spinning-disk confocal, deep tissue-penetration and intrinsic optical sectioning from 2-photon excitation, and a large field of view and a low invasiveness of a selective-plane illumination microscope – all with a single objective lens. We validate the performance of our 2-photon spinning-disk microscope in various applications that have in common to simultaneously require a large depth penetration, high speed and larger fields of view. Beyond biological fluorescence, we demonstrate an application in material science, imaging coherent non-linear scattering from a 3-D nano-porous network

The ability to observe traces of biological material on buildings and stone artworks is of particular importance in understanding how to best deal with them and maybe, in the future, even make use of biofilms for conservation science. We have identified hyperspectral imaging as a viable method for the efficient analysis of such biological materials. Thanks to the high throughput of our approach based on an interferometric method based on Fourier Transform, we were not only able to detect traces of biofilms on stone samples, but also to map in which areas these were found to have higher biological activity.

The study of the interaction of biological tissue with polarized light leads to relevant information of physical properties (dichroism, retardance and depolarization) of samples. Polarimetric analysis of different characteristics in tissues is useful for applications such us tissue classification, contrast enhancement or pathology detection. By means of polarimetric imaging techniques we can characterize the polarimetric signature of biological samples in a noninvasive and nondestructive way. We have found that depolarization information is of special interest in turbid media such as plant tissue. In this manuscript we use polarimetric observables for plant inspection. In particular, we provide enhanced visualization of certain plant pathologies by constructing depolarization based pseudocolored images of pathological leaves where the pathological areas are revealed.

Freeform Optics enables the design of more compact or more complex optical systems. Here, we will demystify designing with freeform surfaces, yet demonstrate their power in optical design. Designing for manufacture is important for affordability, and this is even more critical with freeform optics due to their complexity. We will seize the opportunity to also discuss the importance of concurrent engineering in designing freeform optical systems. Finally, we will briefly introduce a novel optical component, the metaform.

Adaptive illumination systems are capable of changing their emission pattern in a dynamic and flexible manner. Such systems can be realized with tunable optical components. We analyze the possibilities and limitations of phase-only spatial light modulators, implemented as a kind of programmable freeform optics, to realize adaptive illumination systems. First, the calculation of the required phase shift patterns to generate specific target irradiance distributions from arbitrary incident wavefronts, is elaborated. Second, the practical limitations of generating prescribed target patterns are experimentally tested and critically discussed.

Freeform metrology is an enabling technology for today’s research and advanced manufacturing. The Tilted Wave Interferometer is a full field measurement system for fast and flexible measurements. It is based on an off-axis illumination scheme based on a microlens array. In this contribution, we present a novel illumination system for the tilted wave interferometer, that allows to reduce the measurement time by a factor of four using parallelization based on wavelength multiplexing. Here we present a design solution that utilizes the flexibility of 3D-printing. The microlenses are realized as multi-order diffractive optical elements, providing a high efficiency compared to colorfilter based realizations. To boost the light efficiency of the novel illumination system further, a field lens functionality is added to the system by adding individual micro-prisms to each microlens. The system is manufactured by the use of grayscale two-photon polymerisation.

Since 1990, adaptive optics are used in astronomy to remove the effects of atmospheric turbulence, and then retrieve diffraction-limited images, even in bad seeing conditions. Thanks to its strong knowledge in Shack-Hartmann wavefront sensing and deformable mirror, Imagine Optic has developed a simple and affordable adaptive optics system for astronomers. We present the current prototype as well as first experimental results on both natural stars and extended sources, with the main goal of allowing an effective correction in all sky conditions regardless of the object.

Modern bio-imaging techniques such as light-sheet, multiphoton and PALM/STORM are now aiming to image more complex biological samples at larger depth and therefore face larger-amplitude and more complex aberrations. We provide an analysis of key requirements driving optimal implementation of adaptive optics (AO) in microscopy, with a focus on wavefront modulators. We show that some specifications of wavefront modulators such as linearity, hysteresis or actuators performance & layout can end up to better AO performance in microscopy systems, when specifically optimized for such use. We then provide design details and characterization results of a newly developed deformable mirror, and report on experimental images obtained from AO-enhanced microscopes based on the device, for several modalities such as light-sheet, multiphoton or super-resolution single molecule localization systems. Finally, we provide recommendations on how to define the right set of AO components, algorithms and overall method depending on modality, instrument and sample constraints.

This paper describes a prospect for broadband mid-infrared (mid-IR) highly coherent supercontinuum generation. Tellurite and chalcogenide glass with high transparency up to the mid-IR range are used as fiber materials. We successfully develop all-solid hybrid microstructured optical fibers made of tellurite and chalcogenide glass to control chromatic dispersion and demonstrate that highly nonlinear soft glass microstructured optical fibers are promising media for broadband mid-IR highly coherent supercontinuum generation.

The advances in fluorescent diamond-based magnetic field sensors have led this technology into the field of fiber optics. Recently, devices employing diamond nanobeams or diamond chips embedded on an optical fiber tip enabled achieving fT-level sensitivities. Nevertheless, these demonstrations were still confined to operation over localized magnetic field sources. A new approach of volumetric incorporation of nanodiamonds into the optical fiber core enables optical fibers sensitive to magnetic field at any point along the fiber length. We show that information on the perturbed spin state of a diamond nitrogen-vacancy color center can be transmitted over a macroscopic length in an optical fiber, in presence of noise from large concentration of the color centers along the fiber. This is exploited in optical readout at the fiber output not only of the magnetic field value, but also spatially variable information on the field, which enables the localization of its source.

Optical fibers that can sustain large elastic deformations are promising building blocks in soft robotics, medical and wearable devices, and advanced textiles. Thus far, however, the fabrication methods developed for soft optical fibers have remained unmatured. Here, we present thermal drawing as a materials and processing platform to fabricate 10s of meters-long soft, multi-material optical fibers with intriguing architectures. It offers unprecedented opportunities to realize step-index soft optical fibers, as well as photonic crystal fibers for transmission, reflection, and sensing.

We report on successful refractive index profiling of commercially available step-index and in-house made graded-index multimode specialty optical fibers by means of X-ray computed microtomography. Our results demonstrate that the latter is an advantageous technique for characterizing large core optical fibers, which allows for retrieving information about the refractive index at optical frequencies by exploiting the absorption coefficient of X-rays.

Adaptative objects based on shape-memory materials are expected to significantly impact numerous technological sectors including optics and photonics. In this work, we demonstrate the manufacturing of shape-memory optical fibers from the thermal stretching of additively manufactured preforms. First, we show how standard commercially-available thermoplastics can be used to produce long continuously-structured microfilaments with shape-memory abilities. Shape recovery as well as programmability performances of such elongated objects are assessed. Next, we open the way for light-guiding multicomponent fiber architectures that are able to switch from temporary configurations back to user-defined programmed shapes. We strongly expect that such actuatable fibers with light-guiding abilities will trigger exciting progress of unprecedented smart devices in the areas of photonics, electronics, or robotics.

Precision spectroscopy of atomic hydrogen provides important tests of bound-state quantum electrodynamics (QED) and searches for new physics. As an independent approach to these tests heavier one-electron atoms can be investigates, as high-order QED terms scale with powers of Z. We aim to measure the 1S-2S transition in He+ with a combination of 790 nm and 32 nm photons using the Ramsey-comb spectroscopy method in combination with high-harmonic generation (HHG). As an important first step towards this goal, we present the first precision measurements using both these techniques on a transition in xenon at 110 nm. The relative accuracy of the measurement of 2.3x10-10 was not hampered by the HHG process and is the highest ever achieved with light generated through this process. A second important step was recently taken with the first observation of laser excitation of the 1S-2S transition in He+ using our unequal photon scheme. In this case, a single 150 fs pulse was sent through a neutral beam of He atoms to ionize them to He+, then excite the 1S-2S transition and ionize the excited ions further to He2+. This paves the way to a precision measurement in a single trapped He+ ion with Ramsey-comb spectroscopy.

We perform broadband cavity ring-down spectroscopy (CRDS) relying on the near-infrared frequency comb as the excitation source and a time-resolved mechanical Fourier transform spectrometer as detection device. The many decays corresponding to each spectral element are recorded simultaneously and sorted after Fourier transformation to yield the CRDS spectrum of CO in Ar contained in a 20’000-finesse cavity.

We present here an experimental demonstration of dual-comb spectroscopy performed around 2 μm, with the use of a new design of dispersion-controlled highly nonlinear fibre. The latter allows us to efficiently convert light via a four-wave mixing process from 1.55 μm to 2 μm, which is a spectral region suited for the detection of pollutants such as CO2 or N2O. Experimental measurements have been performed with these two molecules and show an excellent agreement with the HITRAN database.

Towards realization of beyond-5G large-capacity and ultrahigh-speed terahertz (THz) wireless communication systems, we have developed InGaAs-channel high-electron-mobility transistor (HEMT) and graphene-channel field-effect transistor (G-FET) plasmonic THz detectors, featured by original asymmetric dual-grating-gate (A-DGG) structures. The A-DGG fingers act as a broadband deep-subwavelength grating coupler that converts incoming THz waves into 2D plasmons in the channel, and their strong hydrodynamic nonlinearities as well as their fast response enable fast, highly sensitive THz detection at room temperature.

In this talk, we review recent advances of the A-DGG plasmonic THz detectors and demonstrate that they are promising for use in beyond-5G wireless communication systems. First, we investigate a new way to read out the photovoltage from the gate electrode of an A-DGG InGaAs-channel HEMT that enables the enhancement of responsivity in proportion to the active area size as well as the impedance matching to 50-Ω interconnection systems. Second, we demonstrate that a new plasmonic THz detection mechanism called “3D rectification effect” in an A-DGG InGaAs-channel HEMT in the gate-readout configuration drastically enhances the responsivity. Third, we reveal that, in an A-DGG G-FET, both plasmonic and photothermoelectric effects coexist as THz detection mechanisms, resulting in the high responsivity and 10-ps-order fast response time.

We report the observation of (ultra)strong light-matter coupling, in the UV spectral region, between optical modes of a metal/dielectric bilayer nanocavity and the electronic excitations of spin-crossover (SCO) molecules. By thermally switching the SCO molecules between their low-spin and high-spin states, we demonstrate the possibility of fine-tuning the light-molecule hybridization strength, allowing a reversible switching between strong- (with Rabi splitting values of up to 550 meV) and weak-coupling regimes within a single photonic resonator. As a result, we show that spin-crossover molecular compounds constitute a novel, promising class of active nanomaterials in the context of tuneable and reconfigurable polaritonic devices.

We have designed and realized all-dielectric lossless nanoantennas, in which a thin SiO2 layer doped with erbium ions is placed inside slotted silicon nanopillars arranged in a square array. The modal analysis has evidenced that the slotted nanopillar array supports optical quasi-BIC resonances with ultra-high Q-factors (up to Q∼10^9), able to boost the electromagnetic local density of optical states in the optically active layer. Up to 3 orders of magnitude photoluminescence intensity increment and 2 orders of magnitude decay rate enhancement have been measured at room temperature when the Er^(3+) emission at about λ=1540 nm couples with the quasi-BIC resonances. Furthermore, by tailoring the nanopillar aspect ratio, the slot geometry has been exploited to obtain selective enhancements of the electric or magnetic dipole contribution to Er^(3+) radiative transitions in the NIR, keeping the emitter quantum efficiency almost unitary. Finally, by computing the angularly resolved electromagnetic field enhancement inside the nanoslot, the nanoantenna directivity has been designed, proving that strong beaming effects can be obtained. Our findings have a direct impact on the development of bright and efficient photon sources operating at telecom wavelength that are of primary importance for quantum nanophotonic applications.

The damage caused by irradiation of crystalline material with ions results in localized volume changes. Here, swelling is utilized to fabricate nanostructured gratings with heights below 10 nm for extreme ultraviolet radiation. Irradiations were performed through a structured layer of photoresist shadowing parts of the sample from a broad ion beam. This enabled much shorter fabrication times than comparable direct write processes with a focussed ion beam. The study presents results from first systematic investigations regarding the fabrication of nanostructured gratings by irradiation of silicon with a broad beam of helium ions with energies of 30 keV. A smaller, scanned beam is used for comparison. Fluence was varied from 0.4 to 7.5×1e16 ions/cm^2 . Fabricated structures were measured via atomic force microscopy. This yielded a controllable method to fabricate shallow gratings with heights in the range of 0 to 10 nm.

We investigated the effect of light on the DNA-driven self-assembly to form hierarchical patterns on two dimensional surfaces. We specifically focused on the self-assembly of DNA-functionalized quantum dots (QDs) onto DNA-functionalized glass substrate while illuminating the surface with a laser during coating process. The region illuminated with a green laser remained uncoated with red-emitting QDs while the not-illuminated region was successfully coated. Next, a red laser whose light cannot be absorbed by the red-emitting QDs did not avoid the DNA-driven self-assembly of the QDs onto glass substrate. Additionally, we demonstrated that silica nanoparticles that had been functionalized with DNA and are not able to absorb the light in the visible regime were again coated on the surface while being exposed to a green laser. These results prove that the absorption of the light is responsible for controlling the binding-unbinding process of QDs. Finally, we added DNA-functionalized green-emitting QDs onto the area that was not coated with red-emitting QDs under the green laser exposure. We observed successful coating of previously uncoated regions with the green QDs. This revealed the viability of our technique for building up hierarchical structures without using, sophisticated, or resource-intensive microfabrication methods.

Chip-scale Terahertz quantum cascade laser frequency combs: recent advanced and applications in near field-nanoscopy

Interfacing FEM analyses with optical design and simulations

Raman-on-a-chip technology

Deformable Phase Plates for Adaptive Optics: A Simple Solution for Correcting Complex Aberrations

LIDAR

In this contribution we will discuss the experimental application of 3D chiral metamaterials as high sensitivity biosensors, exploiting circular dichroism in transmission. 3D metamaterials with chiral features can be realized by highly accurate and highly localized bottom-up nanofabrication approach. Large chiroptical effects can be engineered, originating from the single element optical resonances, but collective interactions in arrayed configurations can play a significant role, further enhancing these effects. Capability of biomarker detection in the femtomolar range is demonstrated even in complex biofluid matrix.

As part of EU H2020 I-Seed project, an active laser-induced fluorescence observation system for Unmanned Aerial Vehicle is envisioned to simultaneously measure, geo-locate and range the fluorescence-tagged sensors. In this work, we present lab-scale experimental results of a light-sheet Scheimpflug ranging system employing the excitation laser source of the fluorescence observation setup to compliment the ranging capability of the complete UAV payload.

This work's objective is to study the feasibility of decoupling temperature and strain out of a $\phi$-PA-OFDR readouts. For this purpose, the readouts will be subjected to a study using several Machine Learning algorithms, among them, Neural Networks. The motivation which underlies this target is the current blockage in the widespread use of Fiber Optic Sensors in situations where both strain and temperature change (e.g. composite manufacturing and integration processes), due to the coupled dependence of currently developed sensing methods. Instead of using other types of sensors or even other interrogation methods, the objective of this work is to analyze the available information in order to develop a sensing method capable of providing information about strain and temperature simultaneously

Scintillation, beam wandering, and phase front distortion are the principal impacts of atmospheric turbulence on laser beam propagation. The aperture averaging concept might be used to minimize the effect for the first two, but the third, which is important for high-speed free-space communications, is significantly more challenging. More than ten years ago, the institute of communications and navigation (IKN) of the german aerospace centre (DLR) conducted optical downlink experiments with JAXA's OICETS/Kirari-Japan to study the optical LEO downlink channel and assess the viability of this transmission technology for upcoming applications. The present work will study and give a comparable insight into simulation and experimental results showing a significant relationship elevation dependency for parameters linked to index-of-refraction turbulence.

Shack Hartmann (SH) Wavefront Sensing (WFS) brings many advantages that has made it a standard in optical metrology, but it has long been limited by its resolution compared to other solutions, such as interferometry.

We will present a new approach to the linearized focal plane technique (LIFT), formerly developed by ONERA, which is based on the combination of standard SH technology with phase retrieval algorithms. Applied on all the spots of the SH wavefront sensor microlens array, it provides information on high spatial frequencies, allows to reconstruct more modes for each microlens and results in a 16-fold improvement (4x in each transverse direction) of the sensor spatial resolution!

We will present how we have optimized and validated the LIFT technology for optical metrology. We will share some measurements performed on extremely complex wavefronts. Finally, we will propose an implementation for industrial applications such as manufacturing and will describe some use cases.

Benefiting from the same advantages as SH WFS -such as robustness to vibrations and atmospheric turbulence, or the ability to easily work at any wavelength- the LIFT technology presents very promising perspectives for optical and freeform metrology and can advantageously replace, at lower cost and better usability, Fizeau interferometry.

We demonstrate how a novel approach for closed-loop Adaptive Optics (AO) specifically adapted to microscopy enables straightforward integration in Light-Sheet and Multiphoton microscopes, as well as fast aberration correction. We present corresponding experimental setups as well as first demonstrations of the benefits of the correction of sample-induced aberrations in zebrafish and mouse brain tissue, with the ultimate goal to enable high-speed, high-sensitivity functional imaging at large depths.

Rapid prototyping methods for the fabrication of polymeric labs-on-a-chip (LoC) are on the rise, as they allow high degrees of precision and flexibility. In this contest, the flexibility of ultrafast laser technology enables the rapid prototyping and high-precision micromachining of 3D LoC devices with complex microfluidic channel networks. In this paper, we describe the realization process of a microfluidic tool for fully inertial particles sorting. The microfluidic network was realized in polymethyl methacrylate (PMMA), exploiting femtosecond laser technology. The multilayer device was assembled through a facile and low-cost solvent-assisted method. In particular, we studied the particle focusing in curved inertial microfluidic channel with trapezoidal cross section. A particles focusing along the walls of the device, sensitive to particle size and flow rate, was observed based on the principle of Dean-coupled inertial migration in spiral microchannel

Sensors based on photonic crystal (PC) surface mode imaging are promising tools for label-free drug screening and discovery, diagnostics, and analysis of ligand–receptor interactions. Imaging of PC surface modes has been demonstrated to allow simultaneous real-time detection of multiple events at the sensor surface. Here, we report the engineering of a lateral-flow microfluidic assay where PC surface mode imaging is used for multiplexed detection of biomolecular targets (antibodies, oligonucleotides, and a DNA repair protein), as well as kinetic data on their interactions obtained without additional labelling or signal amplification. Our data demonstrate the suitability of the biosensing platform designed for ultrasensitive, quick, and low-cost detection and monitoring of interactions between different biomolecules.

We report on the development of Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) technology to detect 8 different air pollutants, namely CH4, NO2, CO2, N2O, CO, NO, SO2 and NH3, with the same acoustic detection module and interchangeable laser sources, to prove the modularity of the technique as well as the adaptability to different lasers. For each gas species, the fine structure of the infrared absorption bands has been simulated by using HITRAN database. Each gas species was detected with an ultimate detection limit well below their typical natural abundance in air even with a signal integration time as low as 0.1 s.

A recent challenge in bioimaging is the observation and imaging of vital, thick, and complex tissues in real time and in non-invasive mode. In the last decade, non-linear excitation microscopy showed several advantages for in-vivo imaging compared to conventional confocal techniques. Nevertheless, deep tissue imaging remains challenging, especially for thick media, due to spherical aberrations induced on focused beams by the tissue. A low numerical aperture objective lens coupled to high dioptric power microlenses, implanted in the tissue, can be beneficial for the reduction of optical aberrations. In this context, we fabricated a system of plano-convex microlenses and microscaffolds on a single chip by means of two-photon polymerization), to be used for non-linear imaging of biological specimens.

THz ATR spectroscopy provides, in a single measurement, the relative number of defects per membrane surface created by oxidative stress generated during photodynamic therapy (PDT), offering early, sensitive real-time information. THz spectroscopy is therefore a complementary technique to established (biological) assays and can be applied to any topic requiring the real-time examination of short-term plasma membrane permeabilization.

Conventional approaches to microscopy record essentially two-dimensional images with a trade between transverse resolution and depth of field. Advances in computational imaging, using engineered point-spread functions have enabled an increase in depth of field, but generally with poor image quality arising from axial variations in the point-spread function. We report how the axial variations in Airy beams can be exploited to enable diffraction-limited, aberration-free 3D microscopy in a single snapshot for imaging of both 3D surfaces and 3D volumes. Localisation microscopy of point emitters enables microscopy with nanoscale nanoscale resolution and when implemented with various exotic point-spread functions this can be extended to 3D imaging. We will show how 3D locational microscopy based on Airy beams can enable much higher emitter densities, which enables the essential high-speed 3D measurement required in applications ranging through fluid dynamics, cardio-vascular monitoring and single-molecule imaging.

Extreme ultraviolet (XUV) light applications are still a very promising field that was heavily enlivened by the definition of the new wavelength for semiconductor lithography within the XUV range. But the detection of XUV light is also important for the exploration in the field of space science (i.e., monitoring the formation and evolution of solar storms) and high-energy physics (i.e., dark matter detection). The advancement of this technology mainly depends on the performance optimization of XUV sources, optical systems and related photodetectors. In this work, the optical design of a high flux XUV setup was simulated and defined to optimise the beam path which is the backbone of the initial evaluation process for the characterisation of luminescent materials under XUV irradiation. Additionally, the paper focused on the conceptualisation and realisation of the experimental setup as well as the alignment of the optical components and the detector calibration.

Concatenated backward ray mapping is an alternative for ray tracing in 2D. It is based on the phase space description of an optical system. Phase space is the set of position and direction coordinates of rays intersecting an optical line. The original algorithm is limited to optical systems consisting of only straight line segments; we extend it to accommodate curved segments. The algorithm is applied to the compound parabolic concentrator, a standard optical system that collects parallel light and reshapes it to a focused beam. We compare the accuracy and speed of the extended algorithm to the original algorithm and Monte Carlo ray tracing. The results show that the extended algorithm outperforms both methods.

We present a novel approach to computing reflectors with a scattering surface in illumination optics. A scattering model governed by a Fredholm integral equation is derived. Solving this integral relation yields a virtual specular target distribution, which we insert into a Monge-Ampère least-squares numerical solver to get a scattering reflector that yields the desired illumination.

We present a novel approach to minimize aberrations in imaging systems. The energy distributions at the source and target of an optical system play a crucial role in designing freeform surfaces through illumination optics methodologies. We quantify the on-axis and off-axis aberrations using a merit function that depends on the energy distributions. The minimization of the merit function yields optimal energy distributions, which subsequently enable us to design freeform reflector surfaces that cause the least aberrations. We validate our method by testing it for two configurations, a single-reflector system with a parallel source to a near-field target, and a double-reflector system with a parallel source to a point target.

Assisted by the ultimate light manipulation properties offered by flat optical devices, we developed different schemes to impart orbital angular momentum on several beams that originate wavepackets with controllable spatial and temporal distributions.

Spontaneous Four Wave Mixing (SFWM) which generates photonic pairs is studied if it is addressed by optical vortices carrying an orbital angular momentum (OAM). We show that the output beams are OAM-correlated and that the entanglement depends on the 4-level scheme used to realize SFWM.

We exploit gas-phase molecules as light-matter interface to store an orbital angular momentum (OAM) or a superposition of OAM states (OAM-based photonic qubits) carried by ultrashort laser pulses. The interplay between spin angular momentum and OAM is exploited to encode the amplitude and spatial phase information of light beams into rotational coherences of molecules. This last is restored on-demand over tens of picoseconds with a reading beam by taking advantage of field-free molecular alignment. The underlying mechanism at the origin of the storage can be interpreted by the spatial structuring of the molecular sample induced by the field. The excitation indeed produces an inhomogeneous spatial distribution of molecular alignment (amplitude & orientation) whose periodical revivals associated with the quantum beatings of the rotational wavepacket enables to restore the spatial beam structure on-demand. The strategy is successfully demonstrated in CO2 molecules at room temperature. Besides applicability as storage medium with THz bandwidth application, the use of molecules as light-matter interface opens new functionalities in terms of optical processing and versatile control of OAM fields.

Fully polarized light, cylindrical vector beams, and beams with opposite orbital angular momentum (OAM) and their superpositions are respectively represented as points on the Poincaré sphere (PS), the higher-order Poincaré sphere (HOPS) and the OAM Poincaré sphere (OAMPS). Here, we study the mapping of inner points between these spheres, which we regard as incoherent superpositions of points on the surface of their respective sphere. We obtain points inside the HOPS and OAMPS by mapping incoherent superpositions of points on the PS, i.e., partially polarized states. To map points from the PS to the HOPS, we use a q-plate, while for mapping points from the HOPS to the OAMPS, we use a linear polarizer. Furthermore, we demonstrate a new polarization state generator (PSG) that generates efficiently partially polarized light. It uses a geometric phase (GP) blazed grating to split an unpolarized laser into two orthogonal polarization components. An intensity filter adjusts the relative intensity of the components, which are then recombined with another GP grating and directed to a waveplate, thus achieving every point inside the PS. The proposed PSG offers advantages over other methods in terms of energy efficiency, ease of alignment, and not requiring spatial or long-time integrations.

Several types of super-resolution microscopy, such as Stimulated Emission Depletion (STED), Reversible Saturable Optical Fluorescence Transitions (RESOLFT) or Switching Laser Mode (SLAM) microscopies, employ Laguerre-Gaussian beams (also called vortex or doughnut beams) to obtain fluorescence information within a sub-wavelength region of the specimen under observation, thus breaking the diffraction limit and producing images of greatly improved quality. However, in general, these techniques operate on a point-by-point basis, so we need to raster scan the sample in order to build a full, meaningful image, which takes time. Parallelization of the illumination is the only way to make these microscopies more suitable for live cell imaging applications. Here, we demonstrate the parallel production of arbitrary arrays of Gaussian and Laguerre-Gaussian lasers foci suitable for super-resolution microscopy, together with the possibility to fast scan through the sample, by means of acousto-optic spatial light modulation, a technique that we have pioneered in the past in several other fields.

In this presentation, we will discuss dissipative Kerr soliton generation on Lithium Niobate and Silicon Carbide microresonators. Additionally, I will introduce inverse-designed nonlinear Fabry-Perot resonators on Silicon Nitride and Silicon Carbide platforms for frequency comb generation

Repetition-rate locking in soliton microcombs via the injection of a weak second continuous-wave laser in the spectral wing of the soliton is studied experimentally, resulting in all-optical control and reduction of phase noise through optical division.

We present a tapered coupler design to achieve single-mode operation in multimode microring resonators and experimentally demonstrate Kerr comb generation in a high-Q, single-mode operated AlGaAs-on-insulator multimode microring resonator.

We report on the formation of temporal solitons in a Kerr fiber resonator that includes a phase modulator shorter than the fundamental limit imposed by the stimulated Raman scattering.

We report the observation of a stable and broadband optical frequency comb in a high-Q fiber Fabry Perot resonator. We evidence it arises from an unexpected mode-locking phenomena.

Flexible and stretchable photonics are emerging fields aiming to develop novel applications where the devices need to conform to uneven surfaces or whenever lightness and reduced thickness are major requirements. However, owing to the relatively small refractive index of transparent soft matter, these materials are not well adapted for light management at visible and near-infrared frequencies. Here we demonstrate simple, low cost and efficient protocols for fabricating Si1−xGex-based, sub-micrometric dielectric antennas with ensuing hybrid integration into different plastic supports. The dielectric antennas are realized exploiting the natural instability of thin solid films to form regular patterns of monocrystalline atomically smooth silicon and germanium nanostructures. Efficient protocols for encapsulating them into flexible and transparent, organic supports are investigated and validated. We benchmark the optical quality of the antennas with light scattering measurements, demonstrating the control of the islands structural colour and the onset of sharp Mie modes after encapsulation.

Flexible glass photonics is a cutting-edge technological and scientific research field that, thanks to a very broad spectrum of applications, has tremendously grown during the last decade and is now a strategic topic. Here, we present the results of the spectral transmittance and reflectance of a 10-layer SiO2/TiO2 1D photonic crystal deposited on a flexible polymeric substrate under different bending conditions, obtained with a home-made adjustable sample holder.

This study introduces an actively switchable wire grid polarizer exploiting the semiconductor-metal transition of vanadium dioxide. Operating at a near-infrared wavelength, the device features a SiO2 substrate with VO2 deposited by atomic layer deposition. We demonstrate the design using rigorous coupled wave analysis and show a viable fabrication route. Polarisation-resolved spectral transmission measurements show switching of the extinction ratio from 37.5 (on-state) to 1.6 (off-state). Despite observed deviations between measured and theoretical transmission values, the device shows potential in miniaturized imaging processes, polarization measurements, and ellipsometry.

Aluminum nitride is a white, hydrophilic, high-band-gap ceramic. Here we report on the light-induced evaporation of saltwater through a capillary wick composed of drop-cast microparticles. Saltwater evaporation rates are significantly higher than expected. Our results point to significant potential for this interface-driven approach in solar non-thermal desalination and water separation technologies.

We measured the photoluminescence (PL) of single CsPbBr3 nanocrystals (NCs) that have a highly anisotropic shape and orthorhombic crystal phase. As the thickness of these NCs is much more smaller than the other two dimensions, they are also called nanoplatelets (NPLs). We obtain PL spectra characterized by doublets separated in energy by about 2 meV in average and showing orthogonal and linearly polarized polar lines. We identified these doublets as the two bright-exciton states of the exciton fine structure contained in the plane of the NPLs. By a comparison between theory and experiments, we were able to obtain fundamental parameters as tetragonal and orthorhombic crystal field. We measured and analysed the time-resolved PL evolution as a function of temperature of small ensemble of NPLs. We thus succeed at framing the experimental value of the bright-dark exciton splitting (5-7meV) that is slightly smaller than the theoretical value.

The scientific community has been exploring new concepts as a result of the usage of optical fibers as absolute measurement sensors. While cross-sensitivity is a common issue with optical fiber sensors, this issue has been mitigated by simultaneous measurement techniques. But when it comes to absolute measurements, these methods have some limitations. The white light interferometer, which offers a superb solution for a range of applications, especially for absolute temperature measurement, is one of the most often used methods for absolute measurements.

This paper proposes a proof of concept for a reflective fiber optic sensor based on multimode interference, designed to measure glucose concentrations in aqueous solutions that mimic the range of glucose concentrations found in human saliva. The sensor is fabricated by splicing a short section of coreless silica fiber into a standard single-mode fiber. By studying the principles of multimode interference and Self-imaging it was developed a sensing head that has a total length of 29.1 mm, approximately equal to the second self-image cycle. This sensing head allowed us to detect low concentrations of glucose (ranging from 0 to 268 mg/dl).

A new approach to detect and analyze transverse acoustic mode resonances (TAMRs), responsible for forward Brillouin scattering in optical fibers, is reported using optical whispering gallery modes (WGMs). TAMRs generate perturbations in the geometry and the dielectric permittivity of the fiber that couples the acoustic and optical resonances. This interaction is exploited to probe opto-excited TAMRs exhibiting an optimal efficiency for detecting low-order TAMRs.

Upconverting particles (UCPs) are building blocks of modern photonics. They cannot be used only as imaging agents but also as contactless sensing units. UCPs have already been used for sensing forces, temperature, mechanical properties, and chemical composition. The sensitivity of the luminescence of UCPs to different external stimulus opens the possibility of using them as multiparametric sensors capable of one-shot description of medium possibilities. However, the use of UCPs for multiparametric sensing is limited because of bias: different external stimuli have an identical impact on the luminescence of UCPs. Bias makes impossible the reliable interpretation of the luminescence generated by UCPs and produces erroneous readouts. Avoiding bias requires the development of new strategies in the analysis of UCPs luminescence when used as sensors. In this work, we demonstrate how a single β-NaYF4: Yb3+, Er3+ UCP within an optical trap can provide unbiased measurements of temperature and viscosity. Decoupling thermal and mechanical measurements is achieved by using the luminescence of coupled states for thermal sensing and the polarization of luminescence for the determination of viscosity. The simultaneous and unbiased temperature/viscosity sensing from a single UCP is demonstrated in a series of proof-of-concept experiments

Applying the inverse-source technique, we have developed an analytical model describing the angular radiation and source-plane spatial-spectral coherence property of white light emitting diodes (LEDs) and demonstrated it experimentally. A corresponding elementary-field representation, which benefits by simplifying the treatment of partially coherent beam shaping and imaging problems, is formulated. Moreover, we identify spectral parts of white LED’s spectrum that follow Wolf’s scaling law of spectral invariance.

We review our recent work on the use of genetic algorithms to control non-stationary nonlinear wave dynamics in ultrafast fibre lasers, including the generation of breathing-soliton dynamics with controlled characteristics, the disclosure of the fractal dynamics of breathers, and the generation of rogue waves with controlled intensity.

We demonstrate for the first time the generation of broadband tunable and synchronized pulses exceeding the microjoule level using the new concept of fiber optical parametric chirped-pulse oscillation (FOPCPO). The oscillator is based on a collapsed-ends photonic crystal fiber pumped in the normal dispersion regime by a fiber laser.

We unveil a strategy for configuring mode-locked fiber lasers by means of a tunable bandpass filter, which allows multi-pulse structures to be generated without distortions in their intensity profiles, with significantly reduced pumping power levels.

Because of the pulse energy quantization in fiber lasers, it is of great importance to find effective

ways to increase the pulse energy directly from a fiber laser. An efficient technique is based on the dissipative

soliton resonance (DSR) effect. The DSR manifest as a square pulse with constant peak power and a linear

increase of both the pulse energy and duration for increasing pumping power. In practice, DSR is favoured

with the use of long cavities. In this communication we propose an overview of DSR in fiber lasers including

general theoretical approaches together with the most recent relevant experimental results

Optical frequency combs are applicable across many fields, especially in metrology. Through accounting for field polarization, the spontaneous symmetry breaking of vector temporal cavity solitons and combs in Kerr Fabry–Perot resonators is presented. This work can improve the generation of frequency combs through its control on the maximum number of soliton-pairs in a round trip and reveals the interesting phenomenon of dominant polarization conformity across all soliton-pairs in the cavity.

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Project iFLOWS aims to develop a novel framework for the effective and uninterrupted screening of postal/courier flows involving all actors across the transport chain. The main concept of iFLOWS is based on a multi-tiered approach to screening of letters and parcels, enhancing cross-organisation collaboration and intelligence and upgrading the threat, illicit material and dangerous substances detection process.

Our project IPN-Bio aims to foster and develop long-term international, interdisciplinary, and inter-sectoral collaboration between Europe, USA, Latin America, and China. IPN-Bio consortium consists of 13 world-leading organizations (4 EU/UK universities, 3 EU/UK companies, and 6 third country partner organizations) from four continents and eight countries working at the frontier of the field with the complementary expertise in the multidiscipline of Photonics, Nanotechnology and Biotechnology.

Transforming imaging with simultaneous light modulation

Many products and devices depend on imaging technology, from projection displays to remote sensors. The EU-funded DYNAMO project hopes to achieve a new paradigm in imaging techniques by creating spatial light modulators which can operate simultaneously. Conventional spatial light modulators operate sequentially: a beam of light is shaped into different patterns, and the time interval between patterns is governed by the refresh rate of the device. Instead, researchers propose sending all patterns in one short nanosecond pulse, creating a dynamic spatiotemporal light modulation device. This will result in ultra-fast imaging with a refresh rate for dynamic pixels equivalent to that of the GHz range.

Objective

Imaging technologies form the basis of a vast range of products and devices and improvements would have a huge impact both scientifically and commercially. We have identified a key bottleneck, how light is modulated in the imaging system, that we can unlock to achieve a new paradigm in imaging technologies. Spatial light modulators, and similar components, operate sequentially: the light beam is shaped in different patterns but the time interval between patterns is limited by the refresh rate of the device. We will remove this limitation, thereby creating a technological breakthrough; our advance will be to send all possible patterns of the device simultaneously, and encoded in a short nanosecond pulse, creating the concept of parallel beam shaping or dynamic spatio-temporal light modulation device. In DYNAMO, we will shape optical beams in two spatial dimensions plus the temporal one. The equivalent refresh rate of the dynamic pixel will start at GHz, although we are confident it will become much higher by the end of the project. To give an idea of our ambition, we compare this improvement in the time to process images with the improvement in the clock frequency of computers: the first general-purpose electronic computer, the ENIAC, had a clock frequency of 100kHz in 1945. It was not until 2000 where AMD reached 1 GHz in their computers. Processing images is broadly similar to processing data so this is indicative of the fifty-year acceleration in the realm of imaging that we will achieve. DYNAMO is an ambitious and integrated project that begins by studying the fundamentals of acoustic wave scattering and ends by developing ultra-fast imaging applications in optics. The success of this pathway requires the synergy of the disciplines of physical acoustics, photonics and imaging. The outcomes from this project offer to accelerate imaging technologies and place European science and industry at the forefront of the inventions and advances that will follow.

V4F aims to show proof-of-principle of a new technology capable of unprecedented control over interactions with specially synthesised targets to significantly improve the energy balance of aneutronic fusion reactions. New concepts and advanced simulations of inertial confinement of aneutronic fusion reactions and particle acceleration will inform pioneering experiments in high-energy matter-interactions. Results could offer the prospect of breakthrough increases in alpha-particle yields from fusion reactions and mitigate the instabilities found in conventional fusion reactions. This work offers the tantalising possibility of aneutronic fusion as a waste-free nuclear energy source and radical new configurations of particle accelerators, leading to an efficient positron beam acceleration. The results will benefit society with game-changing new approaches to clean, safe energy production and significant downscaling of positron accelerators with dramatic impacts in medicine, industry and fundamental science.

Plasmonic nanostructures with achiral, but asymmetric shapes can exhibit chiro-optical phenomena at the nanoscale, given that the nanostructure-light interaction symmetry is broken. Such behaviour is defined as extrinsic chirality, and it is induced by properly arranging the experimental set-up. We show measurement techniques for extrinsic chirality in low-cost, asymmetric samples with nanostructures organized in metasurfaces. We employ widely tuneable chiro-optical characterization of transmission and reflection, as well as the circular polarization degree of the transmitted signal; near-infrared range (680-1080nm) and oblique incidence allow for the detection of resonant features in extrinsic chirality. Other, unconventional experiments use photo-thermal consequences of chirality governed absorption in metasurfaces. Photo-acoustic spectroscopy directly gives circular dichroism as a differential absorption of the left and right circular polarizations exciting the sample. Photo-deflection spectroscopy gives additional information of diffraction phenomena governed by the extrinsic chirality. We showed that these techniques can monitor the extrinsic chiral behaviour of the hybrid plasmonic metamaterials. Moreover, they can be used in combination with fluorescence-detected circular dichroism to measure the emission properties of fluorescent materials.

Circular dichroism spectroscopy is a key probe of the structural and optical properties of chiral materials, however, commercial circular dichroism spectrometers are large, prohibitively expensive and rarely offer environmental control of the sample under test. Here we demonstrate two low-cost (<£2,000) and portable imaging systems controlled by our own bespoke open-source control software which are capable of spatially mapping the circular dichroism of chiral solid state films. By coupling these imaging systems with a temperature controlled stage, we show that we can rapidly identify the thermal processing conditions required to maximise circular dichroism in chiral solid state films by measuring circular dichroism in situ during thermal annealing of a sample under test. The accuracy and spatial resolution of these circular dichroism imagers are cross-compared against our previous studies using an existing circular dichroism imaging system at the Diamond Light Source and are shown to be in good agreement, with a sensitivity down to 250 mdeg and a spatial resolution of 100 μm.

Lattice resonances, collective electromagnetic modes supported by periodic arrays of metallic nanostructures, produce very strong and spectrally narrow optical responses. Recently, there has been significant effort devoted to exploring their chirality (dissymmetric response to right- and lefthanded circularly polarized light) in arrays built from complex unit cells. In this communication, we investigate the lattice resonances of square bipartite arrays in which the relative positions of the nanostructures can vary in all three spatial dimensions, i.e., 2.5- dimensional arrays. Despite the achirality of their unit cell, the lattice resonances supported by these systems can display an almost perfect chiral response and very large quality factors due to the constructive and destructive interference between the electric and magnetic dipoles induced in their nanostructures. Our results provide the fundamental understanding to achieve strong chiral lattice resonances in structurally achiral 2.5-dimensional periodic arrays.

Exotic light fields combining non-trivial spin and angular momentum may not be eigenstates of either the spin or orbital angular momenta operators. For these fields, it is relevant to define a Generalized Angular Momentum operator of which they are eigenvectors. Their associated eigenvalues can take, depending on the case, non-integer values.We report that this new quantity is conserved via non-linear phenomena, such as High Harmonic Generation.

Understanding high-order harmonic generation (HHG) from solid targets holds the key of potential technological innovations in the field of high-frequency coherent sources. Solids present optical nonlinearities at lower driving intensities, and harmonics can be efficiently emitted due to the increased electron density in comparison with the atomic and molecular counterparts. In addition, crystalline solids introduce a new complexity, as symmetries play a role in the anisotropic character of the optical response. An extraordinary playground is, therefore, the scenario in which solids are driven by vector beams, since crystal symmetries can be directly coupled with the topology of the driving laser beam. In this contribution we analyze the topological properties of the HHG radiation emitted by a single-layer graphene sheet driven by a vector beam. We show that the harmonic field is a complex combination of vortices, whose geometrical properties hold information about the details of the non-linear response of the crystal. We demonstrate, therefore, that the analysis of the topological structure of the harmonic field can be used as a spectroscopic measurement technique, paving the way of topological spectroscopy as a new strategy for the characterization of the optical response of macroscopic targets.

In this work we show Frequency Comb (FC) and short pulsed operation of mid-infrared Interband Cascade Lasers (ICLs) in a single long section. This is through the use of an adapted ultrafast Quantum Well Infrared Photodetectors (QWIPs), and correlating the microwave beatnotes with high resolution spectra of the ICL. In particular, we will show active mode-locking (ML) of single-section ICL that does not require RF optimisation of the ICL device and highlight its temporal characteristics using Shifted Wave Infrared Fourier Transform Spectroscopy (SWIFTS) analysis to reconstruct the intensity in the time domain.

We report on a multi-GHz repetition rate, femtosecond fiber laser operating in the burst mode, achieved by nonlinearly shaping and amplifying a phase-only modulated electro-optic comb at 1.03 μm. The system delivers an average power of 1.2 W with pulses compressible down to sub 100 fs.

Electro-optic frequency-comb is an interesting method for comb generation as it offers the possibility to electrically tune the generated frequency-comb by simply tuning the electrical signal applied on the modulator. Integrated modulators operating in a wide spectral range in the mid-IR have been demonstrated recently, relying on free carrier plasma dispersion effect in a Schottky diode embedded in a Ge-rich graded SiGe waveguide. Such integrated mid-infrared modulators have been used to generate electro-optic frequency-combs with more than 200 lines around the 8 µm wavelength optical carrier.

We present a planarized waveguide cavity with an integrated broadband output coupler that improves both the output power and far-field properties of THz quantum cascade laser frequency combs. The laser mirror reflectivity can be tuned by the shape of the end facet, which is obtained with an efficient inverse design algorithm, where the structure is iteratively updated to match the desired figure of merit. Surface emission is achieved with a broadband patch-array antenna, and all the components have been optimized for octave-spanning emission spectra (2-4 THz). Experimentally, we demonstrate a broadband surface-emitting THz quantum cascade laser frequency comb with optical bandwidths of up to 800 GHz, surface emission into a narrow beam with divergence below (20° x 20°) and a peak power of 13 mW.

This paper reports the development of a dual-comb spectroscopy system based on gain-switched single-mode laser diodes emitting at 1572 nm. The switching is performed by a train of short electrical pulses at a repetition rate of 100 MHz while the lasers are subjected to external optical injection. Under these conditions, broad and flat optical frequency combs (OFC) are generated, showing 100 tones within 10 dB and a line spacing fixed by the repetition rate of the switching pulses. The dual-comb generated by the interference of two such combs with slightly different line spacing, is used for measuring the absorption line of CO2 at 1572.02 nm. The transmission spectrum is analyzed and fitted to a Voigt profile. A deviation of 3% in the residuals of the fitting is obtained, denoting the high spectral performance of the spectroscopy system.

While the opportunity to perform fast and broadband spectroscopy in the Mid-IR portion of the electromagnetic spectrum is very appealing, it requires the use of compatible light-sources. Here, we strongly modulate a Mid-Infrared Quantum Cascade Laser at a frequency in the RF domain, which is low compared to the natural repetition frequency of the device. In this way, we demonstrate that it is possible to obtain an emission bandwidth of up to 250𝐜𝐦−𝟏. Finally, we employ it as a light source in an FTIR based on a rotational delay line, performing fast and broadband FTIR spectroscopy.

We report on a polarization-resolved study of mid-infrared emission properties of Er3+ ions in the orthorhombic YAlO3 crystal. For the 4I11/2 → 4I13/2 transition, σSE reaches 0.20×10-20 cm2 at 2919 nm (for light polarization E || c). Pump-induced polarization switching between the E || b and E || c eigen-states is observed in an 10 at.% Er:YAlO3 laser. Pumped by an Yb-fiber laser at 976 nm, this laser delivers 0.77 W at 2919 nm with a slope efficiency of 31.4% being close to the Stokes limit and a laser threshold of 33 mW.

In the present work, a 3-Dimensional diffusion model is proposed to predict the main properties of Diffractive Optical Elements (DOEs), recorded in photopolymers, including refractive index modulation and the evolution of the transverse intensity distribution. The model enables the selection of appropriate material characteristics based on the intended application of the DOE. Specifically, a PVA/AA photopolymer based on acrylamide is simulated using the proposed model, considering coverplating and index matching systems to mitigate the effects of thickness variation. In order to compare its properties using the suggested model, the simulation focuses on a Fibonacci Lens and the dependece of the intensity by the polymerization rate. Accordingly, axial intensity pattern is represented to prove the bifocal-behaviour of these diffractive lenses.

Ultra-Low-Expansion glass (ULE®) has become an important technological enabler of advanced imaging for astronomy and for extreme-UV lithography. A major limitation though, is that ULE® cannot be poured from the fluid state unlike ZERODUR® which renders costly to produce large and/or complex shapes from it. Beside mirrors, optical components are rarely made of ULE® despite it sharing many properties of pure fused silica glass. Here we explore how femtosecond laser processing combined with laser induced reflow can be used to structure ULE® glass with the goal of producing miniature optical components. To fulfil optical roughness requirements, we adopt a strategy based on first producing elementary shapes, such as cubes or cylinders, that we further topologically transform into sphere, ellipsoids or curved surfaces, using a laser-reflow process. The structural modification of the glass matrix induced by the reflow were investigated using Raman spectroscopy. Our result points to a densification of the glass but no apparent sign of crystallization or devitrification. Furthermore, to understand whether the thermo-mechanical properties were affected or not, the thermal expansion coefficient was estimated using a dilatometry technic based on a pseudo-bimorph micro-cantilevers in a temperature-controlled chamber.

Responsive hydrogel photonic structures were fabricated using two-photon lithography. The design versatility of two-photon lithography provides for unprecedented manipulation of transmittance and reflectance spectra, producing distinct structural color. Hydrogel photonic structures have potential for wide range applications, in this instance we demonstrate examples of color transformation, reversible vapor sensing, and pH detection.

Probing buried interfaces in thin films is a crucial task in many fields, including optical coating. Ultrafast acoustics provide a means to characterize the interfaces by using an acoustic wave localized on the nanometer scale. We provide a brief overview of our thorough study of the interface between SiOxNy thin films and Si substrate by using both single-color and broadband picosecond acoustics. The experiment allows us to track the effect of stoichiometry on the acoustics wave propagation and transition over the layer-substrate interface. To optimize the experiment, we also created simulations to study the effect of optoacoustic layer thickness. We show that the used Ti layer features an optimum thickness between 5-10 nm to reveal details of the interface properties.