High Power Laser Frequency Conversion Technology

High power and high efficiency have always been one of the development directions of lasers.In the process of using nonlinear crystals for laser harmonic conversion,the phase mismatch caused by the temperature gradient of nonlinear crystals is a key factor affecting conversion efficiency.This paper mainly conducts simulation research on the temperature field caused by a variety of laser beams passing through nonlinear crystals and its effect on harmonic conversion efficiency,and conducts preliminary laser frequency doubling experiments under theoretical guidance.It has certain guiding significance for the design of frequency conversion of high-power lasers.In this paper,based on the characteristics of Gaussian laser beams and high-power laser beams,the principle of frequency conversion and related technologies(frequency doubling,sum frequency,difference frequency and optical parametric amplification),the effect of phase matching of the crystal temperature gradient during laser frequency conversion is analyzed..Using a variety of laser beam(circular,elliptic Gaussian and super-Gaussian,square,rectangular super-Gaussian)models,the finite element analysis method was used to compare the temperature field distribution of different laser beams with different radius through the frequency conversion of LBO crystal,and the temperature gradient was calculated The resulting phase mismatch affects the overall efficiency of harmonic conversion.The results show that when the rectangular super-Gaussian beam passes through the crystal,the temperature distribution of the crystal is more uniform,and the temperature gradient of the crystal is the smallest;the temperature effect of the rectangular super-Gaussian beam is the least when performing nonlinear frequency conversion.Small,but the optical density concentration is weaker than the circular beam,and the frequency conversion efficiency is low compared to the circular beam.When the laser center light intensity is determined,the high-power laser(corresponding to a large-diameter beam)nonlinear frequency conversion,due to the large temperature difference and temperature gradient in the crystal,the harmonic conversion efficiency is significantly reduced,so the high-power laser frequency conversion,To fully consider the effect of temperature.On the basis of simulation analysis,an intra-cavity frequency-doubling structure is adopted,and the LD double-end pump pumps Nd:YVO4 crystal to design a laser for frequency-doubling laser experiment.In the experiment,the fundamental frequency optical power output reached a maximum of 27 W,and the pump conversion efficiency was 46.5%.Using LBO crystal for intra-cavity frequency doubling,using 1064 nm laser 20% transmittance coupling coupling output mirror,when the Q-switching repetition frequency is 50 kHz,the highest output of 8W 532 nm laser and 8W 1064 nm laser can be obtained at the same time.The harmonic conversion efficiency of the internal laser single pass LBO crystal is 10%.When using a 1064 nm laser all-inverted 532 nm anti-reflection coupling output mirror,the maximum output is 13 W of 532 nm laser power.