Study On High Power Ho:YAG MOPA And Long Infrared OPO Laser System

2?m and 8-12?m wave band,which belong to the atmospheric transmission window range and eye-safe range,have important applications in the fields of laser guidance,directed infrared countermeasure,environmental monitoring and laser medical treatment.Especially in the military field,the demand for high average power,high repetition rate,compact 2?m laser and 8-12?m laser is more and more urgent.Therefore,it is necessary to study 2?m laser and 2?m pumped long-infrared 8-12?m laser.In this thesis,for the purpose to obtain high-power 2?m laser output and 8-12?m laser output,the dual-end-pumped Ho:YAG master-oscillator power-amplifier?MOPA?system,2.1-?m pumped long-infrared ZnGeP₂?ZGP?optical parametric oscillator?OPO?and 2.1-?m pumped long-infrared BaGa₄Se₇?BGSe?OPO are studied theoretically and experimentally.This paper firstly introduces the investigation progress of the methods to achieve high power 2?m laser output.The advantages and disadvantages of these methods are discussed,and it points out the necessity of study on Ho:YAG MOPA system.In addition,the commonly used long-infrared nonlinear crystals are further introduced,and the advantages and disadvantages of ZGP and BGSe crystal in realizing long-infrared laser output are discussed.Then the research progress of ZGP OPO and BGSe OPO in long infrared laser output is introduced,and it is clear that the study of long-infrared ZGP OPO and BGSe OPO is of great significance.The Ho:YAG MOPA system is studied theoretically.The rate equations of the dual-end-pumped Ho:YAG oscillator and amplifier are established.The influence of different parameters on the output characteristics of oscillator and amplifier is simulated.The rate equation of active Q-switching is established,and the effects of different parameters on the output pulse energy and pulse width of Ho:YAG laser are analyzed.According to the steady state heat transfer equation,The thermal distribution in Ho:YAG crystal at high pump power is analyzed theoretically.Equivalent thermal focal length in Ho:YAG crystal is calculated.By dividing the crystal into several parts,the distribution of seed laser spot in Ho:YAG crystal is analyzed.According to the theoretical analysis of Ho:YAG MOPA system,the MOPA system including Ho:YAG oscillator,first and second Ho:YAG amplifier is designed and tested.The oscillator obtained an average output power of 55.1 W at repetition rate of 10 kHz,and the beam quality factor is about 1.1.The influence of different parameters on the output performance of Ho:YAG amplifier is discussed by using the 2.1?m laser as seed laser.The first amplifier achieved an average output power of 140 W at 2.1?m,corresponding to an extraction efficiency of about 60.1%.The second Ho:YAG amplifier was further studied.The influence of different seed laser power on the output characteristics of amplifier was discussed.The second Ho:YAG amplifier obtained an average output power of 231 W at 2.1?m,corresponding to slope efficiency of 67.8%and extraction efficiency of 60.7%.The beam quality factor was less than 1.1.The long-infrared ZGP OPO is studied theoretically and experimentally.The phase matching tuning curves,spectral gain width,pump source limitation and effective gain length of ZGP crystal are analyzed theoretically for Type-I and Type-? phase matching ZGP OPO respectively.The influence of different parameters on the output performance of long-infrared ZGP OPO is analyzed.Experimentally,type-I phase matching ZGP OPO achieved an average output power of 3.3 W at wavelength of 9.7?m and repetition rate of 10 kHz,corresponding to optical conversion efficiency of 3.3%.The power of the idler at the wavelength tuning range of 9.3-9.85?m was more than 2.6 W.The type-? phase matching ZGP OPO achieved an average output power of about 3.4 W at wavelength of 9.7?m and repetition rate of 10 kHz,corresponding to optical conversion efficiency of 3.4%.The power of the idler at the wavelength tuning range of 9.3-10.8?m was more than1.27 W.The type-? phase matching long-infrared BGSe OPO is studied theoretically and experimentally.The phase matching tuning curve of 2.1?m pumped BGSe OPO is calculated,and the wavelength tuning performance of type-? phase matching BGSe OPO in the idler wavelength range of 8.2-9.0?m is studied experimentally.The spectral gain width,pump source limitation and effective gain length of BGSe crystal are calculated.The output characteristics of 2.1?m pumped BGSe OPO are numerical analyzed,and the effects of different parameters on the output characteristics of long-infrared BGSe OPO are discussed.Experimentally,the BGSe OPO obtained an average output power of 314 mW at idler wavelength of 8.93?m and repetition rate of 1 kHz,corresponding to slope efficiency of 7.4%and optical conversion efficiency of 3.5%.The wavelength tuning range of the type-? phase matching BGSe OPO was 8.2-9.0?m.The experimental results of BGSe OPO show that BGSe crystal has the potential to achieve high-power and high-efficiency long-infrared laser output,and 2.1?m pumped BGSe OPO is an effective way to achieve long-infrared laser output.