Design and evaluation of laser sources with high-quality wave fronts

Abstract

The design and evaluation of laser sources that have high-quality wave fronts with minimal residual aberrations and irregularities are described. Two such sources have been developed-a collimated reference source and a point reference source. The collimated reference source provides a collimated wave front with a wave-front irregularity of <0.01 wave rms over a 6-mm clear aperture. Collimation is better than 0.067 wave peak to valley, with an angular ray departure of <1.75 x 10(-5) rad. The point reference source provides a diverging wave front with a wave-front irregularity of <0.01 wave rms over a 0.60 numerical aperture and 0.005 wave rms over a 0.35 numerical aperture. Source wavelengths are 670, 780, and 820 nm. These laser sources may be characterized in terms of their fourth-order wave-front polynomial coefficients by using the testing methods developed in this paper. Once characterized, the sources are used as a known input for testing the optical response of unknown systems. This enables complete characterization of an unknown system in terms of aberration polynomials or other criteria of interest when used in conjunction with a wave-front sensing interferometer. These sources are used to evaluate an equal-path, phase-modulated Mach-Zehnder interferometer. Applications include general-purpose laboratory sources as well as tools for evaluating the accuracy of optical systems.