Deformable mirror characterization using novel Phase Tilted Interferometry method

Abstract

High-accuracy calibration of a deformable mirror is important for the wide range of applications where adaptive optics is used in the feedforward mode or for introducing a precise phase diversity term. While phase shifting interferometry (PSI) can be used for such calibration, it requires expensive equipment and/or cannot be performed on-tool due to space limitations. In this presentation, we demonstrate our novel phase retrieval method from several interferograms with introduced arbitrary tilts (phase tilting interferometry) applied to the calibration of a membrane deformable mirror. As the tilts can be introduced manually by simply misaligning the reference mirror, our method represents an inexpensive and easy-to-use alternative to PSI. The method first exploits global information to establish the phase tilt parameters using the Zoom FFT to determine the maxima location in the Fourier spectra of the interferogram differences squared. Then, it retrieves the phase locally using the least-squares approach. To decrease the noise print-through in the estimated mirror response functions, linear regression is used on the phases retrieved for several values of the actuator voltages.