Diode-pumped passively Q-switched mode-locked c-cut Nd:GdVO4 laser with a GaAs coupler

By using a GaAs wafer simultaneously as saturable absorber and output coupler, a diode-pumped passively Q-switched mode-locked (QML) c-cut Nd:GdVO4 laser is realized in a V-type folded cavity. The repetition rate of the Q-switched pulse envelop increased from 40 to 190 kHz as the pump power increased from 1.92 to 5.72 W, and a maximum Q-switched and mode-locked fundamental mode average output power of 375 mW was obtained. The mode-locked pulse inside the Q-switched pulse has a repetition rate of 143 MHz, and its average pulse width is estimated to be about 700 ps. Using a hyperbolic secant function method, a rate equation model for Q-switched and mode-locked lasers was introduced, in which not only the Gaussian distribution of the intracavity photon density and the influences of the continuous pump rate were considered, but the stimulated radiation lifetime of the active medium as well as the excited-state lifetime of the saturable absorber were taken into account. The numerical solutions of the equations are in good agreement with the experimental results.