| Recently, Cr2+:Zn Se laser has attracted wide attention from researchers. Cr2+:Zn Se laser is widely tunable at 23μm field and has a broad absorption band, which allows it to be pumped by many kind of lasers. Gain-switched Cr2+:Zn Se laser with high energy output could be desired pump source for optical parametric oscillators（OPOs）. The wavelength of Cr2+:Zn Se laser is at the atmospheric window, which means it could be applied to gas detection, remote sensing, Ladar and optical communication. Moreover, Mid-IR laser could be used in medical operation for there are many absorption lines of water molecule and human tissue at this wavelength range. This paper mainly studied the gain-switched Cr2+:Zn Se laser by taking advantage of actively Q-switched Ho:YAG laser and as pump sources, respectively. In the theory part, we started with the energy level structure of Cr2+:Zn Se, and then gave the rate-equation model of it, we analyzed the influence of pattern matching to the laser threshold and output power by deriving the rate-equation. We also analyzed the thermal effect by calculating the temperature distribution in the crystal, then obtained the refractive index profile in crystal by using the thermal refractive index coefficient, and gave the beam propagation matrix of the thermal effect of crystal. Then we introduced the building process of gain-switched pulse, and gave the rate-equation and boundary conditions for the numerical simulation of gain-switched laser. In the experiment part, we first studied the CW Cr2+:Zn Se laser by using Tm-doped fiber laser as pump source, and took the influence of thermal lens effect into our consideration. We designed a three-mirror fold cavity and a four-mirror fold cavity to reduce the inpact of thermal lens effect, and the stable region of three-mirror fold cavity and four-mirror fold cavity were calculated by Matlab, we also studied the influence of thermal lens effect to the beam radius in cavity, as well as the influence of cavity length of four-mirror cavity. Pumped by a Tm-doped laser, the maximum output power of three-mirror fold cavity and four-mirror fold cavity was 4.58 W and 3.67 W, respectively, corresponding to the slope efficiency of 41% and 31%, respectively. Then we investigated the gain-switched Cr2+:Zn Se laser by using the activelyQ-switched Ho:YAG laser as pump source, we obtained the maximum output power of 5.5W and 5.4W at the pump repetition frequency of 2k Hz and 5k Hz, respectively, Corresponding to the pulse energy of 2.75 m J and 1.08 m J, respectively. The slope efficiency was 19.6% and 19.4%, respectively. We also studied the influence of pump energy on the pulse profile and pulse width, we obtained a shortest pulse width of 29 ns. The output laser wavelength was measured between 24502570nm, the beam quality factor M2 was calculated to be 2.8. The output laser wavelength was limited to 2570.5nm with a line width of 1nm after we used a VBG in the cavity, corresponding to a maximum output power of 2.41 W and a beam quality factor M2 of 2.83. |
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