Abstract

Three level lasers are arguably the simplest optical systems capable of the experimental realisation of rich dynamical behaviour over broad operating conditions.^[1-3] Through the experimental investigations we report here, of a three level optically pumped laser, we provide critical tests for the extensive theories of these systems regarding their predicted nonlinear dynamical behaviour. Our findings are, however, in marked contrast with many of the theoretical predictions. Notably the observed instabilities are far more extensive in their dynamic form ranging from timescales of a few nsec to several μsec, on variation of the laser pump intensity. In particular for some conditions we find full amplitude periodic spikes directly from the onset of lasing threshold, which are strongly indicative of homoclinic orbits associated with sustained relaxation oscillations, while at high pump powers instabilities are manifested as high frequency limit cycles associated with coherent Rabi effects. Representative examples of digitised time series obtained from a near resonant cw single mode ¹⁵nh₃ (11.76 μm) laser pumped by a single mode 50 W CO₂ laser are shown in Fig. 1. The transformation in dynamics is found to be a sensitive function of NH₃ gas pressure and gas mixture used, though homogeneously broadened condition is maintained throughout.

© 1992 IQEC