Carole Deumié

Multiscale roughness in optical multilayers: atomic force microscopy and light scattering

We have previously shown that macroscopic roughness spectra measured with light scattering at visible wavelengths were perfectly extrapolated at high spatial frequencies by microscopic roughness spectra measured with atomic force microscopy [Europhys. Lett. 22, 717 (1993); Proc. SPIE 2253, 614 (1994)]. These results have been confirmed by numerous experiments [Proc. SPIE 2253, 614 (1994)] and allow us today to characterize thin films microstructure from a macroscopic to a microscopic scale. In the first step the comparison of light scattering and atomic force microscopy is completed by optical measurements at UV wavelengths that allow us to superimpose (and no longer extrapolate) the spectra measured by the two techniques. In the second step we extract multiscale parameters that describe the action of thin-film coatings on substrate roughness in all bandwidths. The results obviously depend on materials and substrates and deposition techniques. Electron-beam evaporation, ion-assisted deposition, and ion plating are compared, and the conclusions are discussed in regard to the deposition parameters. Finally, special attention is given to the limits and performances of the two characterization techniques (light scattering and atomic force microscopy) that may be sensitive to different phenomena.

Ellipsometry of light scattering from multilayer coatings

A scatterometer is extended and allows us to perform ellipsometric measurements on scattered light in each direction of space. Experimental data are given for single thin-film layers and optical coatings and reveal unexpected results. The phenomena are investigated by means of the electromagnetic theories of surface and bulk scattering that emphasize the role of partial correlation and localized defects.

Angle-resolved ellipsometry of light scattering: discrimination of surface and bulk effects in substrates and optical coatings

Angle-resolved ellipsometry of light scattering is an original technique developed at the Fresnel Institute to identify scattering processes in substrates and multilayers. We extend the investigation because numerous experimental results proved that the technique can be of major interest for analysis of microcomponents and their scattering origins. Surface and bulk effects can be separated in most situations, as well as the oblique growth of materials and the presence of first-order contaminants.

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.

Colorimetric properties of the light scattered by various objects

The artificial reproduction of some coloration effects (for instance nacre aspect, iridescence) which appear spontaneously in the nature needs a right description of the different mechanisms which are involved in these phenomena and especially, a detailed analysis of the spectral behavior of the light scattered by such surfaces. With this aim in sight, we have developed a dedicated set-up for the recording of the reflectance distribution function of solid samples in the whole visible spectral range. We have also analyzed the different methods which are able to describe the color information for scattered light. First experimental results obtained on some organic glass windows are given in conclusion.

ANGLE-RESOLVED POLARIMETRIC PHASE MEASUREMENT FOR THE CHARACTERIZATION OF GRATINGS

A goniometric ellipsometer is used to recover the optogeometrical parameters of metallic gratings. The phase difference between TE and TM polarizations in all the diffracted orders is measured as a function of the incidence angle. The groove depth, together with the refractive indices of all the media of the diffracting structure, is determined for a holographic sinusoidal aluminum grating. It is shown that a thin layer of alumina on top of the grating must be considered.

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.

Determination of refractive indices of opaque rough surfaces

The refractive indices of optical materials are usually determined from spectrophotometric and ellipsometric measurements of specular beams. When the roughness of the interfaces increases, the energy in the specularly reflected and transmitted beams decreases and scattering becomes predominant. For strong roughness (compared to the incident wavelength) a surface does not exhibit specular reflection or transmission, making difficult the determination of the refractive index. We describe two techniques, based on scattering measurements, that one can use to determine the refractive indices of opaque inhomogeneous media.

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.

Interferential powders for the spectral control of light scattering

Optical interference coatings usually offer large possibilities for the spectral control of specular reflected or transmitted light. In this aim, multilayer structures are calculated and realized according to each specific application. These kinds of components are deposited over plane substrates, or on substrates with large curvature radius. In this paper we show how multilayer components can also be deposited on micro spheres to reach other applications connected with the spectral control of light scattering.