Evolution of the beam quality factor for various active medium positions within a Gaussian cavity

A 2-m-long plane-parallel cavity with a Gaussian reflectivity mirror has be en 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 radi ation after reflection on the Gaussian mirror, has been analysed for variou s active medium positions within the cavity. It is shown that in cavities o f equal length and effective Fresnel number, the properties of the intracav ity radiation are dependent on the Gaussian mirror distance from the active medium, since the onset of laser action. Indeed, it has been found that th e beam quality factor M-2 reaches smaller values by setting the Gaussian mi rror closer to the active medium. It is also shown that a theory formerly d eveloped for the evolution of the parameters of Schell-Gauss model beams pr opagating in Gaussian-mirror cavities provides a satisfactory description o f experimental results. (C) 2001 Elsevier Science B.V. All rights reserved.