High-repetition-rate and high-energy laser frequency conversion is critical for applications in scientific research, industrial processing, and energy development. However, achieving high conversion efficiency under high average power is severely limited by crystal material constraints and significant thermal effects, which degrade both beam quality and conversion efficiency. This study presents the development and experimental validation of a second-harmonic generation (SHG) system for a 1 μm laser operating at a high repetition rate of 100 Hz.
To address the challenges of low fundamental peak intensity and pronounced thermal effects resulting from high average power , Lithium Triborate (LBO) was selected as the nonlinear medium due to its large effective nonlinear coefficient, low linear absorption, and inherently high laser damage threshold. The system utilized non-critical phase matching (NCPM) at a working temperature of 150 °C to enhance environmental adaptability and angular acceptance bandwidth. Furthermore, beam contraction techniques were applied to increase the fundamental peak intensity and minimize the internal temperature gradient by shortening the heat flow path. To counteract efficiency degradation caused by laser-induced dynamic temperature rise, a pre-compensation method adjusting the crystal to the optimal phase-matching angle for thermal equilibrium was implemented.
Experimental results demonstrated an SHG output energy of 2 J at a wavelength of 532 nm, with an excellent energy stability of 1.2% (RMS). The conversion efficiency reached 54% utilizing a fundamental input of 3.7 J at 100 Hz. Although the achieved efficiency was slightly lower than theoretical predictions—primarily attributed to fundamental wavefront distortions, beam divergence, and residual spatial temperature gradients—the study successfully validated the steady-state thermal simulation models and the dynamic temperature compensation methodologies for high-average-power frequency conversion systems.

second harmonic generation,thermal effect,material nonlinearity