Method for measurement of realistic secondmoment propagation parameters for nonideal laser beams

Abstract

A method is proposed for the assessment of meaningful second-moment propagation parameters for real laser beams aberrated by widely scattered light in their transverse irradiance profiles. The method relies primarily on the curves describing the propagation parameters as functions of the fraction of the total beam power enclosed within the limits of integration of the second-moment integrals. Rapid changes in the propagation parameters as the fractional power content approaches unity clearly indicate the presence of widely scattered outer wings or noise in the beams' profiles. The values taken by the propagation parameters in the region where the rapid changes begin to manifest themselves are expected to give the realistic propagation parameters for the analysed laser beam. The method is demonstrated using irradiance profiles measured from a He−Ne laser beam, and allows for an educated aposteriori assessment of the propagation parameters without using any predetermined numerical criteria for the limits of integration of the second-moment integrals.