Research On OPO Conversion Efficiency Based On Inverse Step Pulse

Compared with expensive Ti-doped sapphire laser,optical parametric oscillator(OPO)has become an effective alternative to obtain "phototherapy window" because of its high skin transmittance and low cost.In this thesis,a method of obtaining inverse step pump pulse based on stimulated Brillouin scattering(SBS)pulse shaping technique is proposed to improve the energy conversion efficiency of OPO.It is of great significance to improve the theory of OPO conversion efficiency,expand the application of SBS technology and high power solid state lasers.The main contents of this paper are as follows:In the theoretical part,based on the one-dimensional transient coupled wave equation of OPO,a finite difference scheme for numerical simulation is constructed,and the effects of the output mirror signal reflectivity,peak power and time domain waveform on the conversion efficiency are analyzed.At the same time,the influence of waveform parameters(duration ratio,power ratio,rising edge time and tail edge time)of inverse step pulse on conversion efficiency is analyzed by means of iso-peak-power diagram and iso-energy diagram,and the selection method of optimal temporal-pulse parameters for high power OPO is given.In the experimental part,based on 7.6 ns,1 Hz and 1064 nm single longitudinal mode xenon lamp pumped lasers,SBS temporal pulse shaping technology is used to obtain inverse step pulse and inverse step pulse pumped OPO experiments respectively.In the SBS experiment,a compact single-cell SBS structure with focusing lens focal length of +300 mm,interaction length of 15 cm and SBS medium of FC-770 is used to obtain a steep-front step pulse with slope efficiency of 79.4%.In OPO experiment,532 nm inverse step pulses for OPO pumping are obtained by combining SBS generator,traveling wave amplifier and frequency doubling crystal.KTP crystal with size of 6×6×10 m3 is selected as the non-linear crystal,phase matching mode is type II phase matching on XZ plane,and double-pass pump structure with Signal reflectivity of 50% is selected to obtain 28.2% signal light output.