Experimental and Theoretical Investigation on Subnanosecond Pulse Characteristics From Doubly QML Nd:Lu0.5Y0.5VO4 Green Laser

Using the mixed crystal Nd:Lu_0.5Y_0.5VO₄ as laser media, an Laser Diode-pumped dual-loss-modulated Q-switched mode-locked (QML) laser generating subnanosecond pulses with adjustable kilohertz repetition rate is presented. This pulse laser system is simultaneously modulated by an electro-optic (EO) modulator and a central semiconductor saturable absorption mirror. Because the repetition rate of the Q-switched envelope in this laser depends on the modulation frequency of the EO modulator, single mode-locking pulse with subnanosecond width exists underneath a Q-switched envelope with kilohertz repetition rate can be obtained. The experimental results show that the pulsewidth of the subnanosecond pulses decreases with the increasing pump power and the shortest pulse generated at 1 kHz was 460 ps with pulse energy of as high as 174 μJ, corresponding to a peak power of 378.3 kW. The rate equation theory is used to describe the dual-loss-modulated QML laser. By considering the Gaussian distribution of the intracavity photon density and the influence of the continuous pump rate, the coupled rate equations for the dual-loss-modulated QML lasers are given. The key parameters are determined, and the numerical solutions of the equations are basically in accordance with the experimental results.