Thermal radiation transferred to the guided modes of optical interference coatings.

An electromagnetic model is developed to predict the thermal radiation which is trapped in a multilayer structure and transferred to its guided modes. The theory is based on the electromagnetic power supplied by the thermal currents given by the fluctuation-dissipation theorem. The source of the radiation is the ambient temperature or that caused by the optical absorption of the component subjected to spatio-temporal illumination.

Power transfer efficiency for obstructed wireless links using Bessel beams.

The power transfer efficiency of a partially obstructed wireless link operating in the Fresnel region is studied in this work. The wireless link consists of two equal apertures, axially aligned, radiating weakly-diffractive beams (truncated Bessel beams). A metallic obstacle is considered along the propagation path of the radiated beam to analyze its impact on the power transfer efficiency with respect to a clear line of sight link.

Photo-induced thermal radiation of optical interference coatings submitted to a spatio-temporal illumination.

We present an electromagnetic model for photo-induced thermal radiation in multi-layer interference filters subjected to arbitrary pulsed illumination with limited beam size. Numerical calculation is used to analyze various structures affecting thermal radiation, such as multi-dielectric mirrors in the mid-infrared range. Other zero-admittance structures are shown to strongly confine and enhance the thermal radiation with an emissivity close to unity at pre-defined frequencies (wavelength and angles).

Frequency-Dependent Squeezed Vacuum Source for the Advanced Virgo Gravitational-Wave Detector.

In this Letter, we present the design and performance of the frequency-dependent squeezed vacuum source that will be used for the broadband quantum noise reduction of the Advanced Virgo Plus gravitational-wave detector in the upcoming observation run. The frequency-dependent squeezed field is generated by a phase rotation of a frequency-independent squeezed state through a 285 m long, high-finesse, near-detuned optical resonator. With about 8.

Instantaneous measurement of surface roughness spectra using white-light scattering projected on a spectrometer.

Following on from previous studies on motionless scatterometers based on the use of white light, we propose a new, to the best of our knowledge, experiment of white-light scattering that should overtake the previous ones in most situations. The setup is very simple as it requires only a broadband illumination source and a spectrometer to analyze light scattering at a unique direction. After introducing the principle of the instrument, roughness spectra are extracted for different samples, and the consistency of results is validated at the intersection of bandwidths.

Low coherence interferometric detection of the spectral dependence of the retro-reflection coefficient of an anti-reflective coated interface.

The measurement of very low reflection coefficients of anti-reflective coated interfaces has become a key issue for the realization of precision instruments such as the giant interferometers used for the detection of gravitational waves. We propose in this paper a method, based on low coherence interferometry and balanced detection, which not only allows to obtain the spectral dependence of this reflection coefficient in amplitude and phase, with a sensitivity of the order of 0.1 ppm and a spectral resolution of 0.

Optical model-based calibration of gray levels for laser damage size assessment.

Fused silica is prone to damage under ultraviolet laser irradiation. Because they are key components to achieve fusion on high energy laser facilities, final fused silica optics are analyzed after each laser shot. The quantification of damage sites is limited by the image resolution.

Photo-induced temperature in optical interference coatings.

The photo-induced temperature in multilayer systems is calculated using an original analytical model based on optical/thermal analogies. Various illumination regimes are considered, ranging from ps pulses to a continuous regime, while taking into account a variable repetition rate. The temporal and spatial (3D) resolutions are quantified, and the distributions of temperature and stationary optical field are compared.

Analysis of the multilayer organization of a sunflower leaf during dehydration with terahertz time-domain spectroscopy.

We apply reverse engineering techniques (RET) to analyze the dehydration process of a sunflower leaf with terahertz time-domain spectroscopy. The multilayer structure of the leaf is extracted with accuracy during the entire process. Time variations of thickness and the complex index are emphasized for all leaf layers (2 cuticules, 2 epiderms, and 2 mesophylls).

Immediate and one-point roughness measurements using spectrally shaped light.

Capitalizing on a previous theoretical paper, we propose a novel approach, to our knowledge, that is different from the usual scattering measurements, one that is free of any mechanical movement or scanning. Scattering is measured along a single direction. Wide-band illumination with a properly chosen wavelength spectrum makes the signal proportional to the sample roughness, or to the higher-order roughness moments.

Micro-cavity optimization for ultra-sensitive all-dielectric optical sensors.

We present an analytical method for the optimization of luminescent micro-cavities to create a substrate that is extremely sensitive to contamination. Giant optical enhancement can thus be controlled arbitrarily and simultaneously at various frequencies within the substrate's evanescent field with the aim of obtaining ultra-sensitive optical sensors. This process provides an alternative to sensors based on illumination in free space.

Mechanisms driving self-organization phenomena in random plasmonic metasurfaces under multipulse femtosecond laser exposure: a multitime scale study.

Laser-induced transformations of plasmonic metasurfaces pave the way for controlling their anisotropic optical response with a micrometric resolution over large surfaces. Understanding the transient state of matter is crucial to optimize laser processing and reach specific optical properties. This article proposes an experimental and numerical study to follow and explain the diverse irreversible transformations encountered by a random plasmonic metasurface submitted to multiple femtosecond laser pulses at a high repetition rate.

Design of multilayer optical thin-films based on light scattering properties and using deep neural networks.

Despite limiting the performance of multilayer optical thin-films, light scattering properties are not as yet controllable by current design methods. These methods usually consider only specular properties: transmittance and reflectance. Among other techniques, design of thin-film components assisted by deep neural networks have seen growing interest over the last few years.

Trapped light scattering within optical coatings: a multilayer roughness-coupling process.

Despite numerous works devoted to light scattering in multilayer optics, trapped scattering has not been considered until now. This consists in a roughness-coupling process at each interface of the multilayer, giving rise to electromagnetic modes traveling within the stack. Such a modal scattering component is today necessary for completing the energy balance within high-precision optics including mirrors for gyro-lasers and detection of gravitational waves, where every ppm (part per million) must be accounted for.

Terahertz probing of sunflower leaf multilayer organization.

We analyze the multilayer structure of sunflower leaves from Terahertz data measured in the time-domain at a ps scale. Thin film reverse engineering techniques are applied to the Fourier amplitude of the reflected and transmitted signals in the frequency range f < 1.5 Terahertz (THz).

A New Optical Sensor Based on Laser Speckle and Chemometrics for Precision Agriculture: Application to Sunflower Plant-Breeding.

New instruments to characterize vegetation must meet cost constraints while providing accurate information. In this paper, we study the potential of a laser speckle system as a low-cost solution for non-destructive phenotyping. The objective is to assess an original approach combining laser speckle with chemometrics to describe scattering and absorption properties of sunflower leaves, related to their chemical composition or internal structure.

Black paints covered with multidielectrics: light absorbers.

Black paints are commonly used to provide broadband light absorbers in high-precision optics. We show how multidielectric coatings improve the performances of these absorbers. The coated rough paints still exhibit a quasi-lambertian diffuse reflection, but this scattering pattern can be reduced by several orders of magnitude, which strongly enhances absorption.

Wide-range wavelength and angle resolved light scattering measurement setup.

We present a new version of a light scattering measurement setup, using a high-power supercontinuum laser source, two volume hologram filters, and two low-noise scientific grade cameras. This configuration enables spectral and angle resolved characterization of the light scattered by complex thin-film filters from 400 to 1650 nm. Measurements carried out on specific filters illustrate the performances of the setup.

Sensitivity of resonance properties of all-dielectric multilayers driven by statistical fluctuations.

In photonics and emerging fields of quantum and topological materials, increasing demands are placed upon the state and control of electromagnetic fields. Dielectric multilayer materials may be designed and optimized to possess extremely sharp spectral and angular photonic resonances allowing for the creation of fields orders of magnitude larger than the exciting field. With enhancements of 10 and higher, the extreme nature of these resonances places high constraints on the statistical properties of the physical and optical characteristics of the materials.

Combining light polarization and speckle measurements with multivariate analysis to predict bulk optical properties of turbid media.

This study aims to investigate the combination of speckle pattern analysis, polarization parameters, and chemometric tools to predict the optical absorption and scattering properties of materials. For this purpose, an optical setup based on light polarization and speckle measurements was developed, and turbid samples were measured at 405 and 660 nm. First, a backscattered polarized speckle acquisition was performed on a set of 41 samples with various scattering (${\mu}_s$μ) and absorbing (${{\mu}_a}$μ) coefficients.

Anti-scattering effect analyzed with an exact theory of light scattering from rough multilayers.

First-order theories of light scattering previously revealed the existence of anti-scattering effects in optical multilayers. Here we present an exact electromagnetic theory that is able to complete the scattering analysis when first-order scattering is cancelled. The theory is valid for arbitrary rough multilayers.

International round-robin experiment for angle-resolved light scattering measurement.

An international round-robin experiment has been conducted to test procedures and methods for the measurement of angle-resolved light scattering. ASTM E2387-05 has been used as the main guide, while the experience gained should also contribute to the new ISO standard of angle-resolved scattering currently under development (ISO/WD 19986:2016). Seven laboratories from Europe and the United States measured the angle-resolved scattering from Al/SiO-coated substrates, transparent substrates, volume diffusors, quasi-volume diffusors, white calibration standards, and grating samples at laser wavelengths in the UV, VIS, and NIR spectra.

Breakthrough spectrophotometric instrument for the ultra-fine characterization of the spectral transmittance of thin-film optical filters.

In this paper, we provide a detailed description of the main features of the upgraded version of a spectrophotometric apparatus developed by our team since 2014 [ Opt. Express23, 26863 (2015)]), and whose improved performance allows the characterization over the visible and near infrared part of the spectrum of the transmittance of complex interference filters with high spectral resolution (approximately one tenth of a nanometer) and an extremely wide dynamic range (thirteen decades).

Terahertz transmission imaging of inhomogeneous polymer multilayers: theory and experiment.

We extend an interferential multilayer model used in optics in the terahertz domain to be able to simulate the mapping of the transmissivity of a multilayer structure of polymers. In particular, we are interested in extracting the thickness gradient of a glue layer within an assembly of polymers. We developed an iterative procedure which we validated by terahertz imaging.

Broadband loss-less optical thin-film depolarizing devices.

For some space applications, sensors are sensitive to light polarization and can only be properly calibrated with non-polarized light. Here we propose new optical devices which allow to depolarize light in a spatial process. These devices are thin film multilayers which exhibit polarimetric phase variations in their plane.