Development Of Nanosecond Mid-infrared Laser Based On PPLN

Optical Parametric Oscillator（OPO）is a tunable laser Oscillator.The optical parametric oscillator（OPO）working in the middle infrared band plays an important role in the fields of laser radar and atmospheric detection.The main work of this thesis consists of two parts.The first is the development of an engineering prototype of nanosecond infrared laser which can output three wavelengths at the same time.The second is the development of a wide-tuned nanosecond mid-infrared laser applied to mid-infrared differential absorption radar.The main contents of this paper are as follows:1.The advantages and disadvantages of traditional laser technology and the advantages and characteristics of frequency conversion technology based on nonlinear optical effect are introduced.The phase matching technology involved in optical parametric oscillator is described,and the principle and realization of quasi-phase matching are emphasized.The principle of optical parametric oscillator is explained and some research progress in China is briefly introduced.2.Based on Maxwell’s equations and the matter equation,a three-wave coupling equation describing the process of optical parametric oscillation is derived,and the parameters such as threshold value,conversion efficiency and wavelength tuning range involved are calculated and explained.3.The development of three wavelength nanosecond infrared laser is introduced.In this work,the engineering prototype can output three wavelengths of 1μm,1.5μm and 3.8μm simultaneously.The pulse width can be adjusted between 100ns-300ns,the repetition frequency can be adjusted between 10KHz and 100KHz,and the maximum output power of 1μm laser is greater than9.6W.1.5um laser is greater than 6.5W,3.8μm is greater than 3.2W,and the total oblique efficiency is 32%.The total weight of the prototype is 19.5kg,and the dimensions are 400mm long,300mm wide and 200mm high.It is small in size and light in weight,so it is easy to carry to the application scene.4.The development of a wide-tuned single-frequency nanosecond mid-infrared laser is introduced.The laser can simultaneously output two nanosecond pulse mid-infrared lasers with pulse width of 5ns,repetition frequency of 250 Hz,pulse energy of more than 1m J and beam quality of 2.5.By switching the periodically polarized lithium niobate crystals（PPLN）with different polarization periods,the mid-infrared laser with the output wavelength covering 2.6μm to 4.4μm can be achieved.The differential absorption concentration of NO₂,SO₂ and NO was measured by the laser.