Quantification of critical alignment parameters for a rotationally-shearing interferometer employing exact ray trace

Abstract

A rotationally-shearing interferometer (RSI) is sensitive to asymmetries in wave fronts. The rotational system, composed of a Dove prism, provides an adjustable sensitivity to the RSI, which is most desirable for asphericity measurements and extra-solar planet detection. We are interested in determining the magnitude of critical engineering parameters that ensure a performance better than λ/10 for the RSI. Previously, we determined that, when the manufacturing tolerance of the angles of a Dove prism is maintained within ±0.35 arcsec, the maximum wave-front deviation is less than λ/10 (at 633 nm). In this work, we study the angular and the change-induced deviations caused by the positioning of the rotational system. We determine, employing exact ray trace, the positioning tolerances and the resolution of the fine mirror movements needed to satisfy a maximum wave-front deviation of λ/10 in the RSI. This analysis shows that the compensating element of the RSI provides a 0.7 arcsec window, wherein the maximum OPD remains below λ/10. Moreover, the positioning tolerance in the RSI must lie within ±0.33 arcsec. The results suggest the use of piezoelectric actuators to control prism and mirror mounts to ensure the desired performance.