Fiber-Optic Phase Shifting Interferometer

To address the MDA need for non-destructive evaluation and detection of surface and subsurface defects in aspheric telescope SiC mirrors, Luminit, LLC proposes to develop a new Fiber Optic Phase Shifting Interferometer (FOPSI). The proposed FOPSI is a non-contact real-time in situ surface roughness monitoring system based on an innovative, modular, highly sensitive interferometer consisting of a movable sensor head and a rapid non-mechanical phase shifting module, using single mode fibers to generate the reference and object waves. A high-speed camera in the sensor head captures a sequence of consecutive interferograms within sub-millsecond time intervals, which are then used to reconstruct the surface profile so that real-time image processing software can detect defects. The lightweight sensor head (<1 kg) can be easily positioned for in situ monitoring and evaluation of a SiC mirror in production. In Phase I Luminit will develop a proof-of-principle FOPSI and demonstrate the feasibility of mapping the surface profile in <5 minutes and detecting defects within 1 micron of a typical 10 inch SiC aspherical mirror surface with an accuracy of 5 nm rms. In Phase II Luminit will develop a full functioning FOPSI for in situ monitoring and evaluation of aspheric telescope SiC mirrors.