Telescope interferometers: an alternative to classical wavefront sensors
2008
Several types of Wavefront Sensors (WFS) are nowadays available in the field of Adaptive Optics (AO). Generally
speaking, their basic principle consists in measuring slopes or curvatures of Wavefront Errors (WFE) transmitted by a
telescope, subsequently reconstructing WFEs digitally. Such process, however, does not seem to be well suited for
evaluating co-phasing or piston errors of future large segmented telescopes in quasi real-time. This communication
presents an original, recently proposed technique for direct WFE sensing. The principle of the device, which is named
"Telescope-Interferometer" (TI), is based on the addition of a reference optical arm into the telescope pupil plane. Then
incident WFEs are deduced from Point Spread Function (PSF) measurements at the telescope focal plane. Herein are
described two different types of TIs, and their performance are discussed in terms of intrinsic measurement accuracy and
spatial resolution. Various error sources are studied by means of numerical simulations, among which photon noise
sounds the most critical. Those computations finally help to define the application range of the TI method in an AO
regime, including main and auxiliary telescope diameters and magnitude of the guide star. Some practical examples of
optical configurations are also described and commented.
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