On the measurement of the complex spatial coherence of a He-Ne laser beam

Abstract

The feasibility of determining by experiment the magnitude and phase of the complex spatial coherence of a laser beam using the recently derived inversion expression for complex spatial coherence is demonstrated. Both magnitude and phase dependence for two laser excitation levels for a wide range of correlation intervals is presented. The ratio of the degree of coherence at the two levels for a continuous range of correlation interval is evaluated yielding results consistent with other known experimental facts. The degree of coherence was found to be lower at the higher level of laser excitation. The use of the inversion expression for the experimental determination of the complex spatial coherence for narrow linewidth beams is pointed out. The difficulty in presently establishing the spatial stationarity of the beam, and its relation to the applicability of the inversion expression are discussed.