Application of an achromatic shearing phase sensor for the alignment of a segmented telescope

An achromatic shearing phase sensor is proposed as a phasing technique for the alignment of segmented telescopes. The sensor is based upon a shearing interferometer using two-wavelength interferometry methods. The two beams are created with a diffraction grating. The diffracted orders are re-imaged such that the pupil plane is focused onto a CCD array with a shear displacing the two orders. The amount of shear is equal to the size of the re-imaged segments. The sensor was measured to have a capture range of at least 5 mum, and an accuracy of 0.3 mum or better. The repeatability was 0.1 mum. The sensor is very sensitive to field dependent aberrations in its optical design but the resulting errors can be calibrated. The sensor is an improvement over similar technologies because it can measure and compensate for segment aberrations with tilt and piston adjustments. The sensor is compatible with many mature interferometry techniques and can be used with extended and broadband sources.