COHERENCE TEMPORAL EVOLUTION IN GAUSSIAN CAVITIES OF DIFFERENT LENGTHS

The temporal evolution of the beam-quality factor M-2 is investigated in plane-parallel cavities of different Fresnel numbers with a Gaussia n reflectivity mirror and applied to a Xe-Cl excimer laser. The Fresne l number is changed by varying resonator length. Laser radiation of hi gher 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 s hown that the Gaussian mirror affects the properties of the oscillatin g laser radiation only at the very first cavity round trips. The near- and far-held spatial characteristics of the laser radiation do not va ry after a few transits inside the cavity. Experimental results are su pported by a theory formerly developed for the evolution of the parame ters of Gaussian Schell-model beams propagating in Gaussian cavities. (C) 1998 Optical Society of America.