Characteristics Of All-solid-state Yb:CaF₂ Laser

The all-solid-state laser can produce high-power steady continuous wave,pulse,frequency doubling and single-frequency laser beam,and has become one of the most promising new generation laser sources by virtue of its advantages such as high conversion efficiency,excellent beam quality,long working life,light weight and convenient.Among the many wavebands of all-solid-state lasers,the 1μm waveband laser is widely used in laser ranging,coherent communication,satellite remote sensing scanning imaging,optical image processing,laser guidance,nonlinear frequency conversion and so on because of its position in the atmospheric transmission window.It is one of the hot spots in the laser field in recent years.In this paper,Yb:CaF₂ crystal is taken as the research object,and the characteristics of passive Q-switched,in-cavity frequency doubling and SESAM mode-locked laser are studied respectively.Based on the Yb:CaF₂ crystal mode-locked laser resonator,and using Nd:YVO4 crystal as the gain medium,a comparative study of mode-locked laser experiments was carried out.The research work is mainly divided into the following four parts:（1）The development and application of all solid-state lasers are reviewed.The research significance and progress of 1μm band frequency doubling laser and passive mode-locked laser are analyzed.The research progress and related applications of some Yb3+and Nd3+ doped laser crystals in 1 μm band are introduced.（2）Based on the basic principles of Q-switching,mode-locking and frequency doubling,the basic principles of laser modulation are analyzed.The principles,advantages and disadvantages of different ways of Q-switching and mode-locking are summarized.The process of passive mode-locked using SESAM is analyzed,and the thermal lens effect and collimation focusing system parameters are calculated.The stability region of optical resonator is analyzed according to ABCD matrix calculation method,and the laser spot size in crystal,pump spot size and SESAM spot size are calculated and optimized to achieve good pattern matching.（3）The characteristics of passive Q-switching and intracavity frequency doubling of Yb:CaF₂ crystal have been studied.A passive Q-switching experiment based on Cr:YAG saturable absorber was carried out in Yb:CaF₂ crystal with the size of 7.5×5×2.9mm3 doped with 5at.%,and the pulse width of 1.82W Q-switched pulse was 80.7ns.LBO was used as a frequency doubling crystal to obtain 1.87W green light output.The dual-wavelength output of the basic frequency light was achieved by inserting the glass etalon in the cavity.After frequency doubling and sum frequency,the three-wavelength green light output at 515nm,516.1nm and 517.2nm was obtained at 0.89W.（4）The passive mode-locking behavior of Yb:CaF₂ crystal is studied,and the gain medium is replaced by Nd:YVO4 crystal on the basis of mode-locked laser operation.A 976nm LD was used to pump a 5at.%doped Yb:CaF₂ crystal with a crystal size of 3×3×3mm3 at a Brewster Angle.Stable mode-locked laser output was obtained,with a maximum average output power of 403mW,a slanting efficiency of 9.2%,a pulse width of 3.4ps,a repetition frequency of 120MHz,and a signal to noise ratio of 72dB at the basic frequency.By analyzing the difference of thermal effect between Nd:YVO4 crystal and Yb:CaF₂ crystal,the resonator is fine tuned.An 808nm LD is used to pump an A-cut Nd:YVO4 crystal with doping concentration of 0.5at.%.The output of 1064.02nm pulsed laser with slant efficiency of 7.0%,maximum average power of 295.4mW,pulse width of 12.1 ps,repetition frequency of 120MHz and signal to noise ratio of 60dB in the basic frequency is obtained.