Experimental Research On High Power Mid-Infrared Optical Parametric Oscillator Based On BGSe

The mid-infrared 3⁵?m band has a very bright application prospect in the areas of laser radar,regional environmental monitoring,medical surgery and defense and military.At present,the main means of obtaining the mid-infrared laser is nonlinear frequency conversion,and the development of nonlinear frequency conversion crystal as a core device plays a vital role.At present,the nonlinear frequency conversion crystals commonly used in the market have the disadvantages of low crystal damage threshold,low light transmission range and small effective nonlinear coefficient,so it is necessary to study nonlinear frequency conversion crystals.The crystals of selenium gallium?BaGa₄Se₇,BGSe?appearing in recent years are considered to be very promising mid-infrared nonlinear frequency conversion crystals.First,it has a very wide range of light transmission,about 0.47¹8?m,and the entire band can achieve tunable output,which means that in addition to the medium wave band application,the crystal has great prospects in the long wave band.Secondly,the damage threshold of the crystal is very high,reaching 550 MW/cm2,which makes it possible to achieve high pump power injection and high power output.Finally,the effective nonlinear coefficient of the crystal is relatively large.The working principle of a 1 kHz Q-switched Ho:YAG laser as a pump source is introduced,and the specific experimental parameters and output data are given in Chapter 4.The theory of double resonance and single resonance is also introduced,including the definition of two resonance modes,the specific physical process and the respective threshold and conversion efficiency.The SNLO software was used to simulate the double-resonant annular cavity optical parametric oscillator?OPO?and the single resonant annular cavity OPO in a phase matching mode.The simulation results of different pump spot sizes,different cavity lengths and different output mirror transmittances were obtained.Includes output power and slope efficiency,pulse width and pulse strength data for signal and idler light.On the basis of simulation calculation,the basic parameters of conducting specific experimental research are obtained,which provides theoretical guidance for the subsequent experimental operation.Based on the simulation results,an experimental optical path was built,and a series of experimental results of double-resonant and single-resonant annular cavity OPO were obtained,including a series of results including output spectrum,angular wavelength tuning curve,pulse width and beam quality,and a comparative analysis.The similarities and differences in the output characteristics of the two different resonant modes of the annular cavity OPO,and try to explain it theoretically.In the experiment,the maximum single-pulse energy of the double-resonant annular cavity OPO is 3.68 mJ,the repetition frequency is 1 kHz,and the total output power is 3.68 W.The single-wavelength beam quality of a single-resonant OPO output is significantly better than that of a dual-resonant output corresponding to a wavelength laser.The output laser line width obtained under one type of phase matching reaches hundreds of nanometers,which is very advantageous for wavelength tuning.A phase-matched double-resonant straight-cavity OPO was built to try to obtain high-power output.Finally,a single-pulse output with a single-pulse energy of 5.12 mJ was successfully obtained.The re-frequency was 1 kHz,and the total output power was5.12 W.The efficiency is over 18%.Finally,the wavelength tuning experiment was carried out on the medium wave BGSe crystal OPO.