Enhanced-Bandwidth Fine-Steering Mirror for Aero-Optics Development

This study addresses two issues in high-energy laser aero-optical applications: 1) the jitter introduced by beam-path turbulence and aircraft motion and 2) the thermal stability of mirror-surface quality parameters. Associated problems include achieving high servo control bandwidth with the optical jitter-compensation elements, on the order of 5 kHz, and maintaining surface figure error of 1/10 wave PV @ 633 nm wavelength. The approach includes a high-bandwidth thermally stable fine-steering mirror (FSM) in conjunction with a high-bandwidth wave-front or tracking detector. The FO35-52-SC-RT2-SF3-HB FSM design concepts include using advanced materials to elevate structural bending mode frequencies to well above the servo bandwidth target. This allows increased servo bandwidth and minimizes CTE differences at key interfaces to maintain flatness over temperature. A unique combination of materials is used, including a silicon carbide mirror substrate. Fabrication and polishing steps are also modified to reduce the mirror deformation associated with final assembly.