The temporal evolution of the beam-quality factor M<sup>2</sup> is investigated in plane-parallel cavities of different Fresnel numbers with a Gaussian reflectivity mirror and applied to a Xe–Cl excimer laser. The Fresnel number is changed by varying resonator length. Laser radiation of higher spatial coherence is provided by the cavity of greater length (2.5 m) and then of lower Fresnel number after the first transit. Indeed, the beam spatial coherence decreases with cavity length. It is also shown that the Gaussian mirror affects the properties of the oscillating laser radiation only at the very first cavity round trips. The near- and far-field spatial characteristics of the laser radiation do not vary after a few transits inside the cavity. Experimental results are supported by a theory formerly developed for the evolution of the parameters of Gaussian Schell-model beams propagating in Gaussian cavities.
© 1998 Optical Society of America
M. R. Perrone, C. Panzera, and D. Diso, "Coherence temporal evolution in Gaussian cavities of different lengths," J. Opt. Soc. Am. A 15, 2138-2145 (1998)