High-efficiency 532 nm generation via phase velocity mismatch optimized second harmonic generation of a nanosecond fiber laser

Abstract

A high-efficiency, high-power nanosecond 532 nm light source is developed by optimizing the interaction between the pumping fiber laser and the focusing optics in a single-pass second-harmonic generation (SHG) configuration. The pumping source is a polarizationmaintaining 1064 nm fiber laser that produces nanosecond square pulses, while the SHG process employs a Type-I noncritical phase-matched LBO crystal. Both simulations and experiments were conducted to optimize the nonlinear crystal length and the lens focal length, as well as the degree of phase velocity mismatch represented by the crystal temperature. Unlike previous studies on SHG, this research highlights the importance of a non-zero phase velocity mismatch for achieving maximum conversion efficiency. With the optimized parameters for phase velocity mismatch, crystal length, and focusing geometry, an SHG conversion efficiency of 79.1% was achieved, marking the highest efficiency reported for a single-pass nanosecond 532 nm SHG configuration. The average output power is 326 W at a repetition rate of 7.14 MHz and a pulse duration of 14.1 ns. The analysis and optimization of phase velocity mismatch and focusing geometry presented in this study could be advantageous for wavelength conversion in high-power or high-intensity light sources across different spectra.