Abstract

Herewith, for the first time, we report the stable self-pulsing in the standing wave alexandrite laser in a short-cavity Fabry-Perrot configuration. It has been observed as well near threshold as much above threshold. It appears that the character of the laser signal totally depends on the choice of the pump wave. In the case of Kr-ion pump laser we usually observe the stable CW action, which is achieved after the transient state of damped relaxation oscillations. In the case of Ar-ion pump laser, in turn, the continuos output is almost impossible to achieve even many times above threshold. Instead, the alexandrite laser exhibits the regular CW pulsations with repetition frequency of order of tens of kilohertz (Fig . 1). We propose the following theoretical description of this unstable behaviour. Since in vibronic regime, the laser action in alexandite crystal is phonon assisted ¹, we have introduced the number of phonons N, active in this action, as the new dynamical variable and we have derived ² the rate equations for the populations of three levels directly coupled by photons and phonons: W - population inversion for lasing levels, n₃ - population of the storage level ¹. $I_{\lambda {\lambda }^{\text{'}}}=E_{\lambda }^{*}{E}_{\lambda \text{'}}$, where E_λ is the electric field of the laser mode λ.

© 1998 IEEE