Characterization of large aperture optical wavefronts using the Power Spectral Density function

Abstract

This paper describes interferometric measurements of large aperture optical components, and the use of Fourier techniques to characterize the data. Fourier analysis leads directly to calculation of the Power Spectral Density (PSD) function. Representing the wavefront in this manner addresses the critical issues of light scattering and diffraction which can limit the performance of high peak power laser systems. High peak power solid-state lasers can exhibit nonlinear amplification of specific spatial frequencies. These phenomena can cause "hot spots", self-focusing and beam break-up. The optical components that comprise the laser system can act as noise sources to seed these effects. As a result, the design of the optical components for these lasers use specifications based on the PSD. These specifications limit the amplitude in the mid-spatial frequency regime of the wavefront from the optical components. Once the PSD is known, the RMS surface roughness can be determined for any range of spatial frequency by integrating the PSD(v) vs. v.