Abstract

Numerical simulations of the mode-locking dynamics of synchronously pumped KCl:Tl°(1) and $\text{L}iF:F_2^{+}$ colour-centre lasers [1,2] in Fabry-Perot and ring geometries are presented. The response of each laser to variation of cavity mismatch is discussed and in particular, their pulse-shaping properties and the conditions required for pulse optimisation and stabilisation. Each of the cavity tuning curves consists of a narrow region of quasi-stationary pulsation, bounded by regions in which the presence of spontaneous emission noise generates episodic phase-wave perturbations, leading to a fundamental pulse jitter [3]. The resulting pulse characteristics are independent of whether the lasers are configured in Fabry-Perot or unidirectional ring geometries, but the detailed pulse shapes and the stability boundaries of the two lasing species differ slightly. Thus, whereas it is possible to minimise the phase-wave fluctuations at the peak of the Tl°(1) tuning curve to generate optimised, quasi-stationary pulses, in $F_2^{+}$ a slight detuning from optimum is required, albeit by only approximately 15%. The equivalent bidirectional ring lasers exhibit regions of quasi-stationary, spontaneously unidirectional lasing, bounded by regions of competitive, bidirectional switching. The physical mechanism governing bidirectional switching is the same as that driving pulse jitter in the Fabry-Perot and unidirectional ring configurations, namely, the passage of spontaneous noise induced phase-waves [4]. Consequently, there is a simple correspondence between the two operating regimes of the bidirectional ring lasers and the quasi-stationary and fluctuating regimes of the other laser geometries.

© 1992 Optical Society of America