ANALYSIS OF LASER-BEAM QUALITY DEGRADATION CAUSED BY QUARTIC PHASE ABERRATIONS

Simple formulas are derived for the degradation in the beam-quality fa ctor, M2, of an arbitrary laser beam caused by quartic phase distortio ns such as those that might occur in a spherically aberrated optical c omponent, a thermally aberrated laser output window, or a divergent be am emerging from a high-index dielectric medium as in a wide-stripe, u nstable-resonator diode laser. A new formula for the defocus correctio n that is needed to collimate optimally a beam with quartic phase aber ration is also derived. Analytical results and numerical examples are given for both radially aberrated and one-dimensional transversely abe rrated cases, and a simple experimental measurement of the beam-qualit y degradation produced by a thin plano-convex lens is shown to be in g ood agreement with the theory.