Claudio PALMA¹ and Gabriella CINCOTTI²

¹Physics Department, Third University of Rome, piazzale Aldo Moro 2, 00185 Rome, Italy, ²Electronic Engineering Department, Third University of Rome, via C. Segre 2, 00146 Rome, Italy

(Received April 25, 1995; Accepted July 20, 1995)

The evolution of relevant beam parameters of a light beam propagating through an iterated sequence of spherical lenses and Gaussian apertures immersed in an active medium is investigated. This structure is a classical model for an optical resonator. The effective size of the field distribution, the beam quality factor and the radius of wave front curvature are calculated as functions of the number of transits. Steady-state values of these parameters are also determined and the dependence of the results on the gain of the medium, the aperture width and the focal length is illustrated. A comparison with the case without active medium is also discussed.

Key words : lasers, propagation, coherence