Research On Optical Bistability And Pulse Output Properties Of Tm,Ho:LLF Lasers

LD pumped 2 ?m solid state lasers are very interesting due to the properties such as compactness,eye-safety and so on,and it has been applied to laser range-finder,atmospheric sensing,and medicine.Compared with other crystals,the Tm,Ho:LLF crystal is a promising medium that produces 2 ?m laser,because of its low threshold and low phonon energy.Based on these reasons,optical bistability and pulse output properties of the Tm,Ho:LLF laser are investigated.First of all,the optical bistability of Tm,Ho:LLF laser is studied.The optical bistability output properties for different cavity lengths are investgated.Meanwhile,the polarization characteristics of the output laser have been analyzed.It is found that,at the cavity length of longer than 55 mm or shorter than 50 mm,the laser operates at ?-polarization.While,at the cavity length of 50-55 mm,the laser is ?-polarized.The single mode optical bistability output for various cavity lengths is achieved.The orthogonal polarization single mode laser can be obtained by selecting cavity lengths(50-55 mm).The polarization-sensitive optical bistability switching can be obtained by controlling the angle of F-P etalon.Moreover,the dynamic behaviors of optical bistability are analyzed.The optical switching based on the optical bistability of Tm,Ho:LLF laser is realized.Furthermore,the factors of affecting the bistable switching are also analyzed.Then,the pulse output characteristics of Tm,Ho:LLF laser are studied.The passively Q-switched Tm,Ho:LLF laser is achieved,using a Cr2+:ZnS crystal as the saturable absorber.The influences of transmissivity and distance between saturable absorber and laser crystal on the output performances are detailly studied.For the transmission of 10%and the distance of 10 mm between saturable absorber and laser crystal,the passively Q-switched laser has optimal output performances.The maximum average output power is 73 mW,the single pulse energy is 13 ?J,and the pulse width is about 1.2 ?s,at the pump power of 1.5 W and the cavity length of 100 mm.To obtain the passively Q-switched mode-locking,the five-mirror cavity is designed.At pump power of 4.36 W,the output power is 145 mW with a slope efficiency of 4.4%.The repetition rate of Q-switched laser is 12.3 kHz with the Q-switched envelope of 0.7 ?s,and the mode-locking repetition rate is 250 MHz.