Thursday, May 21, 2015

HiCAT: alignment of the first deformable mirror

Last summer, Sylvain Egron and Lucie Leboulleux aligned the HICAT testbed with more than 15 components, achieving an excellent optical quality: 12±3 nm rms wavefront error over a 18mm pupil. At that time, the 2 Boston kilo-deformable mirrors (DM) were not available and the interns instead introduced two flat mirrors in the optical train of the testbed. Last fall, we received both science-grade DMs and one of them was characterized by Johan Mayozer and Mamadou N'Diaye.

HICAT after first DM alignment
HICAT with the DM device aligned in its optical train.
Picture taken on 05/21/2015 by M. N'Diaye.
Last week, RĂ©mi Soummer and Mamadou N’Diaye inserted the first DM on the HICAT optical train with careful alignment. They first used the 4D Fizeau interferometer to check the optical quality of the bench before removing the flat mirror. They then replaced the latter with the DM to align it. After two days of intense efforts, they finalized the alignment and obtained similar optical quality of the wavefront error before and after DM insertion: 14 and 15nm rms (for the first 36 Zernike modes).
The next step will now consist to reduce the total wavefront errors below 10nm rms by possibly minimizing the residual low-order aberrations (defocus, astigmatism, coma, spherical aberration) via modification of the DM shape. Such improved optical quality will help us to develop and test novel wavefront control algorithms for direct imaging and spectroscopy of extrasolar planets with future missions.

Kudos to Rachel Lajoie (lab manager), Joe Hunkeler and the ITSD team, the facilities team for helping out with IT infrastructure in the lab. Thanks also to Kelly Coleman for procurements.

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