AAS 207th Meeting, 8-12 January 2006
Session 118 TPF Instrumentation
Poster, Wednesday, 9:20am-6:30pm, January 11, 2006, Exhibit Hall

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[118.01] Wavefront Estimation with an Imaging Spectrograph

D.C. Fabrycky, D.N. Spergel (Princeton University)

Direct imaging of extrasolar terrestrial planets will require wavefront control and correction, even for space missions such as the Terrestrial Planet Finder Coronagraph (TPF-C), because of the vast brightness contrast and small angle between star and planet. Phase and amplitude aberrations within the telescope scatter a field of speckles onto the dark regions of the image plane, overwhelming the signal of planets with the noise of stray starlight. For characterization of discovered planets, TPF-C will have an imaging spectrograph onboard; we propose an efficient way to use that instrument to measure the wavefront aberrations so that a deformable mirror (DM) can compensate for them. Part of the starlight's wavefront passes through a phase shifting element, acquiring a wavelength-dependent phase shift, then interferes with the rest of the wavefront at the imaging spectrograph, producing a set of nearly monochromatic images. The differential phase shift creates the needed diversity to recover phase information from intensity measurements, so only one exposure and no DM motion is needed. Once the wavefront is estimated and corrected, perhaps after a number of iterations in a closed loop, the interfering light can be shuttered for a deep exposure with the same instrument. Simulations of imaging spectrograph datacubes, using this technique to estimate the wavefront, provide a proof-of-concept. With these simulations we investigate optimization algorithms which relax assumptions and account for Poisson noise and incoherent light from planets and exozodiacal dust. We thank Princeton University for support.

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