A 2-m-long plane-parallel cavity with a Gaussian reflectivity mirror has been applied to a XeCl discharge chamber with a 35-cm-long active medium and the temporal evolution of the main parameters of the intracavity laser radiation after reflection on the Gaussian mirror, has been analysed for various active medium positions within the cavity. It is shown that in cavities of equal length and effective Fresnel number, the properties of the intracavity radiation are dependent on the Gaussian mirror distance from the active medium, since the onset of laser action. Indeed, it has been found that the beam quality factor M2 reaches smaller values by setting the Gaussian mirror closer to the active medium. It is also shown that a theory formerly developed for the evolution of the parameters of Schell-Gauss model beams propagating in Gaussian-mirror cavities provides a satisfactory description of experimental results. © 2001 Elsevier Science B.V. All rights reserved.

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