High Speed Grating Shear Interferometry for Fast Steering Mirror Characterization

Abstract

Several terrestrial and aerospace applications require the ability to track a Fast-Steering Mirror’s (FSM) high velocity slew rates with microradian positional resolution. Using theoretical analysis and Monte Carlo simulations, the Fast Linescan Grating Shear Interferometer (FLGSI) was designed to meet this demand with commercial off-the-shelf (COTS) parts. The primary goal of this thesis was to demonstrate that the calibrated FLGSI could constantly track the relative FSM position while the FSM was driven with sinusoidal and square electrical waveforms. The angular magnification, the grating period, and the source wavelength affected the measurement resolution of the FLGSI. The FLGSI design had better than -0.5 waves of coma and less than 0.75 waves of spherical aberration (at 632.8 nm) for the ±4 mrad system FOV. With a photon noise model corrected by measured results, the FLGSI propagated uncertainty was less than 9.5 µrad when measuring the FSM angular position with FSM velocities below 1.5 rad/s, and when measuring a stationary FSM, the FLGSI could measure FSM movements as small as 49.22 nrad (twice the FLGSI measurement uncertainty). The OIM 202 was modeled to estimate the mirror velocity, and design experiments to test the FLGSI measurement capabilities. The secondary goal of this thesis was to measure the OIM 202 movement properties with the FLGSI and compare them with the modeled and manufacturer reported properties. The FLGSI, with a framerate faster than 40 kHz, accurately tracked the FSM position when the FSM was moving at rates slower than 1.1761 ± 0.58 rad/s. The FLGSI measured the FSM X-axis settle time to be 9.98 ms with a pointing accuracy of ±1.38 µrad and the FSM Y axis settle time to be 6.69 ms with a pointing accuracy of ±0.94 µrad. The settle time was slightly slower, and the pointing accuracy was slightly worse than quoted manufacturing specifications.