Myriam Zerrad

Statistical signatures of random media and their correlation to polarization properties

A single procedure based on speckle statistics is proposed to identify the scattering origins of light (surface or bulk). Successful results are obtained with high-scattering samples, which offers complementary techniques for imaging or characterization in random media. The speckle statistics are shown to be correlated to partial polarization. Angle-resolved ellipsometric data confirm all conclusions.

Multimodal scattering facilities and modelization tools for a comprehensive investigation of optical coatings

Losses due to the scattered light are known to be a key limitation of optical components performances. Hence a challenge consists in identifying and quantifying the scattering sources with high accuracy. In this context, dedicated techniques and facilities were developed at Institut Fresnel. Numerical and metrological platforms dedicated to light scattering characterization and modelization were created and are be presented in this paper.

Optical characterization of an unknown single layer: Institut Fresnel contribution to the Optical Interference Coatings 2004 Topical Meeting Measurement Problem

We present the characterizations performed at the Institut Fresnel for the Measurement Problem of the Optical Interference Coatings 2004 Topical Meeting. A single layer coated on a fused-silica substrate of unknown composition and parameters is analyzed in terms of optogeometrical parameters, uniformity, and scattering. We determine the refractive index and the average thickness of the coating, then provide the localized determination of the thickness with a 2 mm spatial resolution. Topography measurements include atomic force microscopy and angle-resolved scattering measurements. These results are completed thanks to a Taylor Hobson noncontact 3D surface profiler.

Lab results of the circular phase mask concepts for high-contrast imaging of exoplanets

Circular phase mask concepts represent promising options for high contrast imaging and spectroscopy of exo-planets. Depending on their design, they can either work as a diffraction suppression system or as a focal plane wavefront sensor. While the apodized Roddier coronagraph uses a π-phase mask to obtain complete suppression of the star image in monochromatic light, the Zernike sensor uses a π/2-phase mask to measure the residual aberrations in the focal plane by encoding them into intensity variations in the relayed pupil. Implementations of the Zernike sensor can be considered in exoplanet imagers such as VLT-SPHERE, Gemini planet imager, Palomar-P1640 or Subaru-SCExAO to enlarge their capabilities. However, such concepts have not been validated experimentally up to now. Our goal is to perform lab demonstration of this concept on our visible coronagraph testbed at LAM and to propose an upgrade design for SPHERE. In this communication, we report on results of lab measurements of the Zernike sensor and determine its sensitivity to small wavefront errors.

CCD-ARS set-up: a comprehensive and fast high-sensitivity characterisation tool for optical components

A comprehensive characterisation tool for optical component is presented here. Based on both light scattering and imaging principles, the CCD-ARS set up allows to separate and study localized defects contribution from the local roughness measurement. The numerical method involved to discriminate intrinsic roughness from the influence of defects is detailed and some results are given.

Optimal design for field enhancement in optical coatings

Multi-dielectric coatings are designed to reach total absorption and maximum field amplification at resonances under total reflection. The design method is analytic and numerical results are given. Comparison with plasmons or thin metallic layers is discussed. Scattering from these coatings is investigated for measurements of amplification.

Complex study of zirconia-silica and niobia-silica composite coatings produced by ion beam sputtering

In this study, we report on our recent progress in research of single layer mixed zirconia-silica and niobia-silica composite coatings prepared by Ion Beam Sputtering technique. All coatings of the same optical thickness were characterized in terms of reflection/transmission spectrometry, X-ray diffraction, atomic force and optical microscopy, optical back-scattering and optical resistance (laser-induced damage threshold - LIDT) in subpicosecond mode. The optical resistance, TIS and LIDT results reveal clear dependence on high refractive index material content in composite coating and its crystalline structure. The results are interpreted and discussed by the means of different models available in literature.

Development of a goniometric light scatter instrument with sample imaging ability

The principle of a new scattering measurement system including a mobile lighting and a fixed CCD array is described. This new system allows a spatially resolved light scattering characterization. Moreover it is possible to separate localized defects contribution from the local roughness measurement. The comprehensive characterization of optical coatings can be performed with this set-up, and some examples will be given.

Dielectric structured components for giant field enhancement

Multi-dielectric coatings are designed to reach total absorption and maximum field amplification at resonances under total reflection. The design method is analytic and numerical results are given. Comparison with plasmons or thin metallic layers is discussed. Scattering from these coatings is investigated for measurements of amplification.

Subpicosecond pulse laser damage behavior of dielectric thin films prepared by different techniques

A new instrument dedicated to laser damage measurement in subpicosecond scale has been developed at the Fresnel Institute (3 ps to 100 fs, 1030 nm). The objective of this work is to realize a comparative study of the behavior of hafnia thin films prepared by different techniques (Reactive Low Voltage Ion Plating, Electron Beam Deposition, Dual Ion Beam Sputtering) under subpicosecond pulse irradiation in the near infra red. Laser-induced damage thresholds are measured for one-on-one procedures. Laser damage setup and first results at 1 ps are presented and initiation mechanisms are studied thanks to damage morphologies and optical properties characterization. Results show a dependence of damage threshold with deposition techniques and so with microstructure of the film.