Validation of a spatial light modulator for space applications

Liquid crystals on silicon spatial light modulator (LCOS-SLM) combine the potential of reflection type spatial light modulators with the compactness and robustness of a single chip. They are used today for beam steering applications, optical beam shaping and laser processing. These devices have a high potential for space applications due to the fact that they allow to introduce any tailored wavefront distortion in an imaging instrument. Then, image reconstruction methods as phase diversity can be used to determine the Point Spread Function (PSF) inflight and, later, to introduce a corrective wavefront distortion to correct possible deviations of the expected optical quality. Among other aberrations, the beam phase control can act on the level of focus. In space optical applications image refocusing is usually performed by means of mechanisms, either by using linear displacement of lenses or rotating wheels with plates with different thicknesses. The compactness and absence of mechanical parts of LCOS-SLM can be of great advantage for these applications. LCOS-SLM can save complexity and weight. It also reduces the risk associated to the wear of moving parts. However, this technology has not been qualified for space applications. Liquid crystal leaks as well as outgassing issues may result as a consequence of a low pressure environment. Thermal issues can also result in loss of device homogeneity and the radiation tolerance should be analyzed. In any case, an exhaustive space simulation test is mandatory to increase the Technological Readiness Level of these devices for their use in space systems. In our work we are showing preliminary test of a commercial LCOS-SLM under thermo-vacuum conditions. These tests are basic calibrations used to evaluate performance and degradation in a simulated space environment. Different calibration procedures are also discussed. This technology, with potential to greatly simplify an instrument design, was included in a proposal for the instrument IMaX+ spectro-polarimeter, to be onboard the mission Sunrise III, within the NASA Long Duration Balloon program.