An overview is given about experiments with a new method for Q-switching lasers at a constant pulse repetition
frequency. It uses inside the laser resonator a Single Crystal Photo-Elastic Modulator (SCPEM). This consists of one
piezo-electric crystal electrically excited on a mechanical resonance frequency. In resonance mechanical stresses are
induced that lead via the photo-elastic effect to a strongly modulated birefringence. Polarized light going through such an
oscillating crystal will experience a significant modulation of its polarization and of transmission through a polarizer.
Suitable materials should not be optically active, as it is for example the case for SiO2, and should allow the excitation of
a longitudinal oscillation with an electric field perpendicular to the travelling direction of the light. Crystals of the group
3m, like LiTaO3 and LiNbO3, proved to be ideally suited for SCPEMS for the NIR- and VIS-region. For the infrared
GaAs can be used.
We demonstrated SCPEM-Q-switching for a Nd:YAG-fiber, a Nd:YVO4-slab- and a Nd:YAG-rod-laser with typical
pulse repetition rates of 100-200kHz, pulse enhancement factors of ~100 and pulse durations ~1/100 of the period time.
Typically the average power during pulsed operation is nearly the same as the cw-power, when the modulator is switched
off. The most stable results were achieved up to now with the Nd:YVO4-slab-laser at 10W average power, 1.1 kW peak
power, 127 kHz pulse repetition rate, and 70ns pulse durations.