Pulse-mode operation of a diode-pumped alkali laser combining a fiber ring cavity

A diode-pumped alkali laser (DPAL) has potential advantages for high-power laser operation due to the high quantum efficiency of alkali elements and the benefits inherent in gas lasers. Particularly, pulse-mode DPALs can be applied potentially in various fields such as range finding and materials processing, but pulse generation in DPALs without using active devices has been largely unexplored. In this study, we report passive pulse generation in a cesium DPAL that integrates a fiber ring resonator. When a narrowband pump wave is coupled into a fiber ring resonator spanning several tens of meters, Brillouin scattering induces the generation of a counter-propagating Stokes wave. Under these conditions, owing to the narrow linewidth characteristics of the cesium gain medium, it was confirmed that the pump and Stokes waves experience differential absorption, which consequently leads to the amplitude modulation of the pump and Stokes waves within the ring resonator. The modulated pump wave induces laser oscillation at 894 nm through the cesium gain medium, thereby generating pulses with a high repetition rate of up to 3.4 MHz and a minimum pulse width of 123 ns. The results of this study are expected to lead to the realization of a cost-effective and compact alkali gain medium-based pulsed laser.