Experiments of Second Harmonic Generation output in Pulsed TEA CO2 Laser

It is always the hot subject to realize the output of high-power laser in the range of 3-5 mu m wavelength. This rang of wave band has greatly important applications in military because it located in the atmosphere window. Generally there are two ways to obtain this range of laser wavelength. One way is through optical parameter oscillation (OPO) from shorter laser wavelength and the other is through second harmonic generation (SHG) from longer laser wavelength. Firstly, the comparison between tow nonlinear crystals ZnGeP2 and AgGaSe2 is conducted for their nonlinear coefficient and damaging threshold in theory. The theoretical results show that the crystal AgGaSe2 is more suitable for the SHG of pulsed TEA CO2 laser. When using pulsed TEA CO2 laser with wavelength of 9.3 mu m to pumping AgGaSe2 SHG crystal, the wavelength of 4.65 mu m is obtained. In the condition of repetition rate 100Hz, the upmost output power of single pulse is up to level of 1W, which corresponding efficiency of SHG is about 6%. The experimental results show that the polarization of laser beam has greatly influence on the SHG output of the crystal. Under the radiation of 3MW/cm(2) from fundamental wave and the right position for maximal SHG output in the crystal, when polarization of laser beam rotates +/- 4.5 degrees, the SHG output of energy decrease about 30%. The research of this paper will make a foundation for further development of mid-infrared laser.