Picosecond laser pulse generation in a monolithic self-Q-switched solid-state laser

We report the generation of laser pulses of 290-ps duration with 8-N pulse energy in single longitudinal mode and single transverse mode in a diode-end-pumped monolithic self-Q-switched Cr,Nd:YAG laser. The most commonly used method of generating picosecond laser pulses is the mode-locking technique. Mode-locking generally requires a light modulator such as an intracavity acousto-optical modulator, dye cell, or external cavity. Proper operation of a modelocked laser also requires critical alignment or precision timing. In semiconductor lasers with high-frequency relaxation oscillations, picosecond pulses can be easily obtained by selecting the first peak of the relaxation oscillation by gain switching [ 11. In solidstate lasers with short cavity length, pulses of 270 ps duration have been produced using electro-optical Qswitching in a microchip laser [ 21. The actively Qswitched laser requires the use of high-speed modulator and high-voltage electronics. Recently, the development of miniature self-Qswitched solid-state lasers [ 3,4] points to a new way of generating short pulses using a much simpler approach. In these self-Q-switched lasers, the functions of the gain medium and saturable absorber are combined into one [ 3,4]. This eliminates the need of the external modulator. By using a Smm-long monolithic cavity consisting of a Nd: YAG laser crystal codoped with chromium as saturable absorber, we have demonstrated the operation of a monolithic self-Qswitched laser that generates laser pulses of several nanosecond duration. Using properly designed cavity parameters for shorter photon lifetime, it is possible to reduce the pulse duration by one order of magnitude. The pulses are expected to have high spectral purity due to the presence of the self-induced loss grating in the cavity containing distributed saturable absorber [ 41. In this paper, we report the generation of picosecond pulses in a diode-pumped monolithic self-Qswitched laser. In a Q-switched laser, the duration of the laser pulse is determined by the ratio, r, of the threshold population inversion levels before and after the saturation of the absorber and by the photon lifetime, TV, of the laser cavity. These parameters are defined as