Experimental Progress and Limitations of Optimal Wavefront Correction in Polychromatic Light


Tyler D. Groff, Alexis Carlotti, N. Jeremy Kasdin


Princeton University


Detecting and spectrally characterizing extrasolar planets using coronagraphic techniques in the presence of quasi-static speckles requires wavefront correction based on estimates of the electric field at the final image plane. In future space observatories this will relax thermal and optical figure tolerances to reach terrestrial planet contrast levels. This is also relevant for ground observatories, particularly the next generation of 30 meter telescopes which will inevitably see large phase and amplitude aberrations at the final image plane from even minor variance in the figure and reflectivity of the segments in the primary optics. To most efficiently use these resources for coronagraphic imaging the wavefront control must make the discovery space and bandwidth as large as possible, both of which require control of phase and amplitude errors. Here we discuss using two deformable mirrors in series to perform this type of correction. Of particular importance is the ability to correct over a larger bandwidth from a narrowband estimate of the electric field at the science camera. This is challenging because the ability to correct becomes more sensitive to both estimation errors and aberrations in the system. We identify the primary sources of these errors and discuss how they degrade performance, and investigate the tradeoff between a larger correction bandwidth and more discovery space. We then show a modification to our monochromatic stroke minimizing wavefront control algorithm to achieve correction over varying bandwidths. We present experimental results from the Princeton University high contrast imaging laboratory that demonstrate advances in broadband suppression. These results are compared to performance in monochromatic light in order to confirm the theoretical limitations.

Attached documents

Lyot2010proc s8 talk GroffT.pdf
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