As it is known well, using of frequency doubling in differential absorption CO<sub>2</sub> laser lidars increases the number of atmospheric gases under the control. Additional improvement in potential and gas analyses accuracy, technical and exploitation parameters has to be waited for with design of frequency doublers with more efficient nonlinear crystals. In this work for the first time detailed investigation results are represented on physial properties of new mixed nonlinear crystals grown in accordance with diagram HgGa<sub>2</sub>S<sub>4</sub>:CdGa<sub>2</sub>S<sub>4</sub>→Hg<sub>1-x</sub>Cd<sub>x</sub>Ga<sub>2</sub>S<sub>4</sub>, phase-matching and potential efficiencies of second harmonic generation, so as on results of experimental investigation of TEA and mini TEA CO<sub>2</sub> laser frequency doubling with it use. In spite of two time lower nonlinear susceptibility coefficients of both parent crystals in comparison with most efficient middle IR crystals high efficiency of frequency doubling is fixed in mixed crystals at room temperature. It is tree time in comparison with frequency doubling with, for example, popular ZnGeP<sub>2</sub> and 5.5 time with AgGaSe<sub>2</sub>. These advantages are reached because realization of optimal non-critical phase-matching by choose of mixing ratio x=0.5, so as 2.3 time higher damage threshold, lower phonon absorption at CO<sub>2</sub> laser wavelengths and lower meanings of refractive indexes at fundamental and second harmonic wavelengths. Exploitation parameters of mixed Hg<sub>1-x</sub>Cd<sub>x</sub>Ga<sub>2</sub>S<sub>4</sub> crystal doublers are not worse than parameters of doublers with well-known crystals.
3~5um mid-infrared laser displaying good atmospheric transmitting properties is mostly used as laser source, in many applications such as remote sensing for air pollution determining. And it is usually obtainable in Second harmonic generation (SHG) in CO<sub>2</sub> laser. In the course of investigation, a homemade nonlinear optical crystal AgGaSe<sub>2</sub>, of the size 7×8×12mm<sup>3</sup>, was used for SHG in tunable TEA CO<sub>2</sub> laser with different wavelengths. And, 12 coherent laser sources in 3~5μm from CO<sub>2</sub> spectrum region 10.6μm~9.2μm were obtained. In our results, phase-matching angles aqre in good accordance with the crystal's cutting. Theory calculating on conversion was made as well, to compare with experimental data which present changes of energy conversion under pump's rising. And in the interest of enhancing energy conversion by means of peaking pulse through cutting tail, a plasma shutter, argon charged in body under normal air pressure, was effectively arranged in experiment. As a result, about 50nS width peak pulse was generated, and up to 10% energy conversion (2mJ, 5.3μm) was achieved against 1% without shutter, both pumping in 10P(20) line.
In the present work, directed toward using differential absorption lidar (DIAL) for measuring concentrations of pollutant gases, a monolithic microprocessor-controlled tuning and triggering system for rapidly tuning a TEA C02 laser is reported. It is shown that it is possible to utilize a high frequency stepping motor and a diffraction grating to rapidly select wavelength over rotational transitions in the 9.2-10.8 jtm region of the laser spectrum. The tuning is performed by applying appropriate signals to the stepping motor, which is coupled to the grating via a precision gear box. The microprocessor controls motion of the motor which rotates the correct angle for a given wavelength together with the grating. Many of pollutants have strong absorption lines in the 9-11 im region, therefore the wavelength tunable transversely excited atmospheric-pressure (TEA) CO2 laser becomes an ideal optical source for DIAL.