Research On High Power And Narrow Spectral Width Of Mid-infrared Optical Parametric Oscillation Technology

Narrow spectral width high power infrared laser has a significant application value in scientific research,civil,military field.In this paper,a narrow spectral width high-power pump source is experimentally studied in optical parametric oscillations and amplification techniques.First,a laser oscillator is built using a side-pumped laser module using the theory of dynamic cavity stabilization.A 28 W laser output has achieved.The beam quality M2 is less than 1.3,the output spectral width is not more than 0.05 nm,and the acousto-optic Q-switched technique is used to obtain 100 ns pulsed laser output with repetition frequency 10 kHz,output power 26 W and output beam quality basically unchanged.Based on the theory of spherical aberration compensation of wave-front beams,a two-stage side-pumped amplifier system is built.Because of effectively controlling the beam quality,after amplification more than 90 W is achieved,beam quality M2<1.4,the pulse characteristics of the laser output is basically unchanged.Then,based on the three-wave mixing equation,the resonant condition,threshold value and conversion efficiency of single resonant resonator of signal light are analyzed.Theoretical study shows that the frequency of the resonant parametric light must be equal to the two longitudinal modes of the resonator.The thresholds of the single resonator are closely related to the resonant cavity length,the pump laser spot size,the effective nonlinear coupling coefficient and the cavity loss.OPO threshold of effective means,including the use of non-linear crystal with a high nonlinear coupling coefficient;increase the pump light diameter;pump light double pass or multi-pass;reduce the resonant cavity length;increase the output mirror of the signal light reflection Rate and reduce the absorption of crystals;long pump pulse and other means.The relationship between the reflectivity of the signal light and the pump power is studied.The theoretical model of OPA is briefly introduced.After that we get the OPO temperature pump width tuning curve and the experiment results show that the output power is 0.7 W,the spectral width is less than 1.12 nm with the beam quality factor M2 is 2.17 and 2.26 in horizontal and vertical directions.At the same time,we study the infrared optical parametric oscillator in continuous wave and obtain the infrared output of CW more than 8W,the conversion efficiency is 20%,and the output spectral width is less than 1.63 nm.The OPA experiment shows that in the first stage,the output power is 2.26 W and the conversion efficiency was 15.6%.The spectral width of the signal do not broaden,and the output power of the second-order amplification was increased to 6.35 W.The total conversion efficiency of the second-order OPA is more than 15.7%,the signal spectral width also did not significantly widen.