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International audience; We investigate the validity of the radiative transfer equation to model transmission of light through an absorbing and scattering medium. Assuming that radiative transfer equation is valid, the inverse scattering problem for non-polarized radiative transfer in one-dimensional absorbing and scattering media is solved using a parameter identiÿcation method. We discuss how to identify the albedo, phase function and extinction coeecient of the medium. We present experimental data that conÿrm that this approach is robust and can be used to make reliable predictions of the behavior of scattering absorbing systems.

International audience; We present a numerical simulation of scattering by one-dimensional randomly rough surfaces. It is based on the use of plane-wave expansions to describe the fields on the surface (i.e. Rayleigh hypothesis). Accuracy and convergence properties of two different numerical implementations are studied. Some examples of results for a dielectric and a metallic Gaussian rough surface are shown to be in good agreement with calculations by a rigorous numerical method. The Rayleigh method appears to be a fast computation tool for dielectric surfaces with slopes of less than.

Two LMJ sol-gel coating specifications shall be checked in the production line: imperfections and the transmittance. The metrology equipments installed in the sol-gel building and used for full scale coated optics are described.

Several French research laboratories set up goniometers allowing BRDF measurements at different laser wavelengths in the infrared. On the effor of the Delegation Generale de l'Armement (DGA/STTC), a round robin set of painted targets BRDF measurements was undertaken, under the ONERA expertise. The laboratories participating in this round robin were the Aerospatiale Matra CCR Suresnes, The IPN SMA-Virgo Lyon, the Institut Fresnel Marseille, and the CEA DAM CESTA Le Barp. The goniometers of the four laboratories are firstly described. The targets studied are seven 5cm diameter painted disks of aluminum or steel, a spectralon reference sample, and a sandpaper sample. We have first demonstrated that the pollution of painted targets with dust has a very weak influence on the BRDF. Before and after each measurement series, the directional-hemispherical reflectance of the samples was measured at ONERA. The measurements have been achieved according to a protocol specifying the sample position and laser probe size. Chosen wavelengths for the inter-comparison are 1.064 micrometers . For both wavelengths, the characteristics of the different goniometers are compared in term of noise and repeatability. The difference between the painted targets BRDF measured with the various devices are relatively limited at 1.06 micrometers , and mainly induced by speckle. More important differences are obtained at 10.6 micrometers , particularly for a BRDF measurement device using an absolute calibration method. In order to explain these differences, few hypotheses are advanced. Information on the absolute accuracy is obtained by the comparison of the measured directional-hemispherical reflectance and the one computed from BRDF measurements.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this paper, we present a numerical study of optical waves scattered by rough surfaces. The calculations are based on the use of plane-wave expansions to describe the reflected and transmitted fields on the surface (also known as the Rayleigh hypothesis). This theory is applied to one-dimensional randomly rough dielectric surfaces, by using a random grating numerical generation. Two methods are recalled for the straightforward numerical implementation of the theory: the Point-Matching Method (PMM) and the Fourier Series Method (FSM). Examples of results for a metallic and a dielectric surface, obtained with the latter method, are in good agreement with calculations by an exact numerical method. It is reported that the FSM has a wider domain of validity but that the PMM has a faster computation time.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The performance of a high-resolution deformable mirror (HRDM) is analyzed for wavefront correction on the CEA high-power laser baselines in France : the Laser Megajoule (LMJ), the Laser Integration Line (LIL) and the Petawatt Aquitaine Laser (PETAL). This study is achieved using monochromatic numerical simulations with the CEA MIRO laser propagation code. When compared to the LMJ deformable mirror used alone, the HRDM located at the L-turn is shown to give equivalent performance at filtering pinholes whereas the HRDM located at injection is less efficient. The use of an HRDM improves the impulse response of the LIL/LMJ main amplifier section. As a consequence, on the PETAL 1ω focal spot, it gives a reduction of factor 2.7 of the radius at 80% of encircled energy and an increase up to 40% of the peak intensity. Finally, maximum mechanical amplitude of 10 nm is numerically evaluated for sinusoidal phase technological defects in the case of the HRDM located at the L-turn.

We present a solution based on the Rayleigh hypothesis. The calculation leads to a matrix system that can be computed to yield the efficiencies of a two-dimensional dielectric grating. The results are compared with previously reported numerical results obtained both with exact theories and with perturbation methods. We show that our method can treat rougher surfaces than can classic perturbation methods.