Quasi-Q-switched mode-locked fiber laser for efficient second-harmonic generation

A fiber-laser platform based on subharmonic cavity modulation was developed to generate quasi-Q-switched mode-locked pulses for efficient nonlinear frequency conversion. The system used a 1064 nm ytterbium-doped fiber ring cavity incorporating an acousto-optic modulator (AOM) and a two-stage amplifier to produce stable high-peak-power pulses. By applying subharmonic modulation, the laser generated quasi-Q-switched mode-locked pulses with enhanced peak power compared with conventional mode-locked operation. These pulses were then frequency-doubled in MgO:PPLN to produce 532 nm green output with improved second-harmonic conversion efficiency. The study showed that subharmonic cavity modulation provides a simple and effective way to enhance SHG performance while maintaining stable laser operation, offering a useful approach for nonlinear optics and high-efficiency pulsed laser.