Self-Q-switched Cr:LiCAF laser

Abstract

We report self-Q-switched operation of a Cr:LiCAF laser for the first time to our knowledge. Self-Q-switching (SQS) refers to the generation of a periodic train of Q-switched pulses from a laser cavity containing only the gain medium. Since SQS does not require any additional elements such as saturable absorbers or active modulators, it is far simpler and lower cost in comparison with other Q-switching methods. In the experiments, SQS operation was observed by using an x-shaped, astigmatically compensated laser cavity which contained only the Cr: LiCAF gain medium. A 140 mW, single-mode continuous wave (cw) diode at 660 nm was used as the pump source. In typical cw operation, the Cr: LiCAF laser produced output powers as high as 50 mW with about 50% slope efficiency. The laser had a diffraction-limited output and had a spectral width of about 0.5 nm near 795 nm. SQS operation could be initiated by fine tuning of the separation between the curved mirrors of the cavity and occurred at several discrete separations of the curved mirrors within the stability range of the resonator. Pulsed pumping of the pump diode, active cooling of the gain medium, and/or misalignment of the cavity end mirrors was not necessary to initiate SQS operation. In the SQS regime, the Cr: LiCAF laser produced about 5 mu s wide pulses at repetition rates between 10 and 30 kHz. The corresponding pulse energies and peak powers were as high as 3.75 mu J and 590 mW, respectively. SQS operation was further accompanied with (i) a decrease in the output power to the 30-45 mW range, (ii) an increase of the spectral bandwidth up to 10 nm (full width at half-maximum), and (iii) a switching of the laser output from pure TEM00 to a structured beam containing higher-order spatial modes. We present detailed experimental data describing the temporal, spectral, and spatial characteristics of the SQS Cr: LiCAF laser, as well as the effect of curved mirror separation on SQS. The power-dependent repetition rate data were further analyzed to estimate the effective small-signal loss coefficient of the saturable absorber action.