Optical resolution of phase measurements of laser Fizeau interferometer

Accurate interferometric measurement of large laser slabs requires spatial frequencies of 1mm/cycle to 33mm/cycle over a 100mm field of view to be passed by the system with no more than 25%loss in modulation. To eliminate noise and artifacts due to strictly coherent imaging, many commercial interferometers employ a rotating diffuser on an intermediate image plane and relay this image incoherently onto a detector. Unfortunately, this process may adversely affect the resolution of the instrument. Through measurement of a sinusoidal phase grating an fused silica step, the transfer function a laser Fizeau interferometer was measured for both a system with and without the incoherent relay system. Results are compared to those predicted by diffraction theory. Studies of the effects of defocus and propagation on the measurement were also made. Using strictly coherent imaging dramatically increases the system's ability to measure features of high spatial frequency and allows the measurement requirements for laser slabs to be met.