Fresnel diffraction effects in the design of high-power laser systems

Abstract

Fresnel diffraction by circular apertures for beams commonly encountered in high-power laser systems is investigated. Striking agreement is demonstrated between experimental results and theoretical calculations for beams with uniform and Gaussian intensity profiles. It is pointed out that Fresnel diffraction patterns produced by circular apertures depend only on the incident wave front and the Fresnel number corrected for curvature of the incident beam, F = a2/λL + a2/λR. This also gives an excellent experimental method for measuring divergence. Methods are discussed for minimizing the occurrence of severe intensity variations and resulting self-focusing problems in high-power laser amplifiers.