Diode-Pumped Nd:YAG Green Laser with Q-Switch and Mode Locking

Gaining of a high peak power in the visible light range from a solid state laser with continuous diode pumping is a challenging task in several applications (high-precision material processing, nonlinear optics and Raman-spectroscopy, medicine, etc.). The technique of modulating the Q-factor of laser cavity (Q-switch) enables growth of the peak power approximately as ┬sp / ┬ph (here ┬sp is the upper laser level lifetime and ┬ph is the photon lifetime in the cavity). When we take a typical Nd:YAG laser, this gain in peak power is about 103104 times. The further growth of the peak power is possible through methods of mode locking of the laser (ML). However, realization of mode-locking together with Q-switch (unlike the case of continuous operation mode) is a technically challenging task: we face a high amplification, almost uncontrollable nonlinear effects, damage of optical elements in the laser, etc. In prior art, the steady mode of generation for Q-switch coupled with mode locking (so called QML) is accomplished with using of two acousto-optic modulators (AOM) in a cavity; one modulator operates in the traveling acoustic wave, and the other modulator has the standing wave (see, e.g., Kuizenga, 1981). Actually, the QML mode is possible when we introduce absorbing elements within the cavity (Herrmann & Wilhelmi, 1987; He et al., 1996; Chen et al., 2001; Agnesi et al., 2001; Pan et al., 2007), but in this case the higher pumping level means a higher pulse repetition rate. Therefore the practical levels of peak power are very moderate.