Realization of inverse saturable absorption by intra-cavity third harmonic generation for efficient nonlinear mirror mode-locking

A technique of suppressing passive Q-switching by inverse saturable absorption in a cw nonlinear mirror mode-locked laser is presented. The nonlinear mirror saturable absorber consists of a second-harmonic generation crystal and a dichroic mirror while the inverse saturable loss is realized by intracavity third-harmonic generation. The inverse saturation reduces significantly the critical intracavity pulse energy for stable, self-starting, self-sustained, and power scalable cw mode-locking. Two LiB3O5 crystals are employed to realize the technique in a diode array pumped Nd : YVO4 oscillator providing a peak power of 918 W, pulse width of 29 ps, and repetition rate of 170 MHz.