Physics – Optics
Scientific paper
Jan 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998phdt.......282m&link_type=abstract
PhD Dissertation, ONERA-Publ-1998-3
Physics
Optics
Active Control, Surface Waves, Telescopes, Diffractive Optics, Adaptive Optics, Perturbation, Noise Propagation, Imaging Techniques, Computerized Simulation
Scientific paper
The images obtained with large telescopes are degraded by perturbations, such as the deformation of the instrument structure. These perturbations could be compensated by an active optical system including a wavefront sensor. Among many existing sensors, we have particularly studied a wavefront sensor based on phase diversity. This sensor retrieves the wavefront from several images recorded at different positions near the focal plane. The phase diversity technique seems well adopted for earth observation with space instruments, due to the easiness of implementation. This technique was proposed a few years ago, but the wavefront sensor properties have not been studied yet, due to the complexity of the data analysis required for the wavefront estimation. We have performed a full study of the phase diversity properties. First, we have studied analytically the noise propagation in the estimated phase. This study is extended by a numerical simulation to the case of a large spectral bandwidth, the phase diversity being sensitive to chromatic effects. The effects of the aliasing, and the gain brought by a phase regularization derived from a phase a priori knowledge, are also studied. These results are confirmed by the an experimental study. This wavefront sensor was then used in an active optics bench, and was compared to the Shack-Hartmann wavefront sensor which has well known properties. This works shows that the phase diversity allows, with a simple implementation, to make accurate measurements of the phase with polychromatic extended sources, and it presents all necessary qualities for the active control of an optics system in a satellite.
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