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Experimental testing of space optics is a mandatory process for investigating the optical performances in conditions close to reality. With the optical requirement level increasing over years, these experimental tests are increasingly expensive and time-consuming. A modeling tool would therefore be an elegant solution to avoid these drawbacks. For this purpose, a multiphysics approach has been used to predict how optics behave under thermal loads. In this paper, experimental surface deformations of a space mirror perturbed by thermal gradients are compared to multiphysics simulation results. The local displacements of the mirror surface have been measured by use of electronic speckle pattern interferometry, and the deformation itself has been calculated by subtracting the rigid body motion. After validation of the thermo-mechanical solution, experimental and numerical wavefront errors are compared.

Different types of polymers are proposed for holographic data storage : photopolymers like PMMA where bonds form or break in the polymer network under illumination, photochromic polymers containing for example azobenzene groups (proposed for high resolution nanolithography), and photopolymerizable systems using inhomogeneous polymerization of one or more monomers for holographic data storage. The material proposed in this work enters in the last family, giving rise to thick phase holograms. The coupling betwween polymerization and diffusion processes is extensively studied in order to characterize the photoinduced microstructuration. Diffusion processes are generated by the concentration gradients due to a disappearance of dye and monomer molecules at different rates in the reactive medium. Creation of gratings with spatial frequencies ranging from 10 to 4000 lines/mm was studied. The formulations are suited to be photopolymerized by illumination around 500 nm, allowing the polymerization of thick samples (thickness of a few hundred microns) with a good optical quality. In order to obtain a reversible process and to improve the storage capicity of the matrix, the medium is doped by a photochromic molecule while the polymerization is used for the photostructuration of the host matrix. The process needs at first the creation of tubular regions corresponding to the highest refractive index of the matrix. By entering in such a fiber, light is guided in the thickness of the material. In each microfiber, bits are recorded in the second stage one after the other one. Several bits can be stored in a same fiber by wavelength multiplexing.

The objective of this work is to demonstrate the correlation between a simple laboratory test bench case and the predictions of the OOFELIE Multiphysics software in order to deduce modeling guidelines and improvements. For that purpose two optical systems have been analyzed. The first one is a spherical lens fixed in an aluminium barrel, which is the simplest structure found in an opto-mechanical system. In this study, material characteristics are assumed to be well known: BK7 and aluminium have been retained. Temperature variations between 0 and +60°C from ambient have been applied to the samples. The second system is a YAG laser bar heated by means of a dedicated oven.For the two test benches thermo-elastic distortions have been measured using a Fizeau interferometer. This sensor measures wavefront error in the range of 20 nm to 1 µm without physical contact with the opto-mechanical system. For the YAG bar, birefringence and polarization measurements have also been performed using a polarimetric bench.The tests results have been compared to the predictions obtained by OOFELIE Multiphysics which is a simulation software dedicated to multiphysics coupled problems involving optics, mechanics, thermal physics, electricity, electromagnetism, acoustics and hydrodynamics. From this comparison modeling guidelines have been issued with the aim of improving the accuracy of computed thermo-elastic distortions and their impact on the optical performances.

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