Utilization of simultaneous loss and phase modulation to mode lock the frequency-doubled Nd: YAG laser

Simultaneous utilization of both loss and phase modulation to mode lock a Nd:YAG laser produces superior performance to that obtained with either modulation technique individually. While the Nd:YAG laser can be mode locked using either phase modulation or loss modualtion, each of these techniques has its inherent disadvantages. Phase modulation allows the possibility of a phase ambiguity in the mode-locked pulse train, while loss modulators rarely have sufficiently large modulation depth, particularly at higher mode-locking frequencies, to produce stable, relaxation-oscillation-free, mode-locked operation. Several techniques have been suggested by various authors to eliminate the ambiguity associated with phase modulation. None of these works well with an internally frequency-doubled laser since intra-cavity frequency doubling encourages the phase ambiguity since by reducing harmonic conversion efficiency. When the laser is mode locked using simultaneous loss and phase modulation, however, the pulse train phase ambiguity is removed and the laser exhibits the desirable characteristics of both mode-locking techniques.