Active and passive stabilization of solid state lasers

Abstract

We present an overview of diode-pumped solid-state lasers with negative feedback stabilization. Active stabilization by means of direct modulation of cavity losses was utilized in several Nd-based quasi-continuous-wave lasers mode-locked by saturable Bragg reflectors (SBR). The stabilization acts to eliminate the relaxation-oscillation-driven spiking after laser oscillation turn-on. Stable continuous-wave modelocking was observed in as little as 10 µs after laser turned on where the leading spike was reduced or completely eliminated dependent on the gain material and the operating wavelength. Stabilization was also used to prevent Q-switching instabilities in a continuous-wave SBR-modelocked Nd:KGW laser resulting in an extended operational parameter range and pulse shortening by up to 35%. Stabilization of passively mode-locked lasers could alternatively be achieved using an intra-cavity element exhibiting nonlinear absorption, which was demonstrated using an Indium Phosphide plate. Pulse shortening by up to 30% was permitted as the modulation depth of the SBR could be increased whilst maintaining stable cw modelocking. Active stabilization was also employed for Tm-based lasers emitting in the 1.9 -2 µm wavelength region as these lasers suffer from inherent amplitude instability and sensitivity to cavity perturbation. Passive stabilization of a Tm:YAlO laser utilizing a germanium plate was also investigated.