Study On 3 ?m Band Laser Characteristics Of Ho³⁺,Pr³⁺ Co-doped Fluoride Crystal

Mid-infrared(MIR)lasers operating at 3 ?m wavelength band have significant applications in the fields such as gas detection,laser medicine,material processing,scientific research,military defense,etc.It has become a hot field for national defense and civil competition research and development.This thesis takes holmium(Ho3+)and praseodylium(Pr3+)co-doped fluoride crystals as the research object,and does a systematic study on the spectral characteristics and laser properties of this kind of crystals.The thesis focuses on the basic research of rare earth fluoride crystals,combining crystal physics and laser optimization design,and exploring the laser characteristics of Ho3+and Pr3lco-doped fluoride crystals in the 3?m band.The detailed research contents are as following1.This chapter starts from the demands and applications of the 3 ?m wavelength band MIR lasers.The applications of the 3?m wavelength band laser in gas detection,laser medical treatment,material processing,military,etc.are introduced.Summarizes the main technical methods of generating 3?m wavelength band laser,summarizes the research progress of rare earth ion doped solid laser,and clarifies the technical difficulties and existing problems.Starting with the activated ion and matrix material in the 3 ?m band,the optimized combination of activated ion and matrix material in this band is analyzed.Finally,the research content and significance of this paper are summarized.(Chapter One)2.The spectral characteristics of Ho,Pr:YLF crystals are analyzed.The results show that the introduction of Pr3+ions can effectively "deactivate" the lower energy level of the Ho3+:5I7 laser,realizing the reversal of the lifetime of the upper and lower energy levels of the 3?m laser.Based on the spectrum and energy level lifetime study,the emission cross section and effective gain cross section of the Ho,Pr:YLF crystal are given numerically,and the feasibility of the Ho,Pr:YLF crystal to produce a 3?m band laser output is analyzed.(Chapter Two)3.Ho3+,Pr3+co-doped fluoride crystal 3 ?m band continuous wave laser characteristics.Starting from the selection of pump sources,the application status of several different pumping methods in this band is compared and summarized.In the experiment,the influence of laser diode(LD)and fiber laser as pump sources on the output power and efficiency of Ho,Pr:LLF crystal laser is compared.Aiming at the problems of low output power(<1 W),that of high power and high efficiency is difficult to rachieved at the same time,the continuous wave laser characteristics of two doping concentration Ho,Pr:YLF crystals are studied,and the maximum output power of 1.27 W and the maximum slope of 28.4%are realized at 2.95 ?m.The results show that the introduction of Pr3+ ions can break through the"bottleneck" of laser oscillation "self-termination" and achieve high-power and high-efficiency continuous wave laser operation;considering a-cut Ho,Pr:YLF crystals have polarized absorption,and the double-end pumping method can improve the uniformity of the heat distribution in the crystal,therefore,the output power of the Ho,Pr:YLF crystal was further explored,and maximum output power of 1.46 W is achieved.With the help of prism tuning technology,the characteristics of Ho,Pr:LLF crystal tuning laser have been studied.The high output power and wide tuning range indicate that Ho,Pr:LLF has the potential to realize ultra-fast laser operation.(Chapter Three)4.Ho3+,Pr3+co-doped fluoride crystal 3 ?m band Q-switched laser characteristics.Based on different Q-switching technologies,nanosecond Q-switched laser operation was realized in Ho3+and Pr3?co-doped fluoride crystals,respectively.Aiming at the problem of poor beam quality and low repetition frequency in the 3?m band electro-optic Q-switched laser,the experiment is proposed by using LN electro-optic Q switch plus double-end pumping scheme to achieve high repetition rate and high beam quality nanosecond pulse laser.In the passive Q-switched pulsed laser experiment,semiconductor saturation absorption mirror(SESAM)is firstly used as the modulation element to achieve 395 ns pulsed laser output.The pulse modulation potential of new two-dimensional materials(graphene,black phosphorus,titanium diselenide)as a saturable absorber in the 3 ?m was explored.(Chapter Four)5.Ho,Pr:LLF crystal 3?m band mode-locked laser characteristics research.Starting from the mode-locking technology,combined with the latest progress of the current 3 ?m band ultrafast lasers,the current difficulties in achieving mode-locked operations at 3?m solid-state lasers are pointed out.In the laser experiment,combined with the research results of the high power and tuned laser characteristics of Ho,Pr:LLF crystals in the previous chapters,the characteristics of continuous wave mode-locked lasers of Ho,Pr:LLF crystals are studied.(Chapter Five)6.Summarize the research contents and innovation points of the paper from the crystal spectral characteristics,continuous wave/pulsed laser characteristics of Ho3+,Pr3+co-doped fluoride crystals,and point out the shortcomings of the paper and the points to be further studied.(Chapter Six)...