Abstract

A grazing incidence interferometer (Gil) using sinusoidal phase modulation was developed at LMSC to sample the surface figure of large deformable mirrors along narrow swaths utilizing small optical components mounted along the periphery of the mirror to control the shape of the mirror. The instrument is described, and results of tests used to calibrate it are discussed. The statistical limitation to the resolution of the figure sensing due to electronic noise and vibration of the optical components was measured to be <10⁻⁴ waves. The actual total resolution was measured by comparing the Gil to a polarization interferometer (PI) in a Ritchey-Common test-bed. The standard deviation of the measured Gil resolution is between 3.9 × 10⁻⁴ and 2.4 × 10⁻⁴ waves. The larger limit of this resolution measurement is set by errors in the PI calibration. The smaller limit is set by examining the error distribution in the best fit between the two instruments and extracting those errors due to the PI.

© 1988 Optical Society of America