Yuri M. Andreev

Parametric frequency converters with LiInSe2, AgGaGeS4, HgGa2S4 and Hg0.65Cd0.35Ga2S4 crystals

Second harmonic generation of 9 μm emission band of CO2 laser is for the first time realized with a number of new nonlinear crystals: biaxial LiInSe2, AgGaGeS4 and uniaxial HgGa2S4, Cd0.35,Hg0.65Ga2S4. For LiInSe2 and AgGaGeS4 it is first type of frequency conversion realized some time or other. Main feature of this crystals is wide range transparency from 0.4-0.6 to 12.5-16.2 μm. Their damage thresholds for 30 ns TEA CO2 laser pulses at 9.55 μm is determined as 1.7 to 2.3 times higher than for popular middle IR crystals such as ZnGeP2 or AgGaSe2. Parmateters of second harmonic generation were determined correctly in comparison with ZnGeP2 crystals at 33 ns pump pulses and intensities that are about 28.5% of damage thresholds of ZnGeP2. As high as 7% external peak power power efficiencies is typical for orange and yellow phases of 3.1 mm HgGa2S4 crystal at such pump that is only 13% of its damage threshold. Efficiencies as high as 0.45% and 0.3% are realized in 2.1 mm AgGaGeS4 crystal at pump intensities that is only 11% of damage threshold. It was determined phase-matching angles, spectral dependence of second harmonic generation efficiencies, so as angular and spectral phase-matching widths that are investigated in details.

Doped GaSe nonlinear crystals

The physical properties of pure GaSe and the crystals doped with 0.01÷3% Al, In, Te, and S have been observed comparatively to reveal the potentials for frequency conversion of laser emission. It has been shown that GaSe:S(greater than or equal to 3%) is the most promising material for practical applications.

Wide band frequency converters for Lidar systems

Estimations are carried out on creation possibilities of all solid state laser sources capable significantly or fully to solve the problem of the universal Aerosol-Gas Lidar System design. Best existing Ho2+:ILF and Nd:YAG lasers supplied with LBO, KTA, KTP, BBO, CLBO, DLAP; GaSe, GaSe:In, AgGaxIn1-xSe2, LiInS2, LiInSe2, AgGaS2, AgGaxIn1-xS2, and HgGa2S4 frequency converters are considered. The investigation results show development of UV to FIR laser source is really to carry out with efficiencies from one-two up to several tens of percent in several ways.

New mixed LiIn(S1-xSex)2 crystals for frequency conversion of IR lasers

LiInSe2 and mixed LiIn(S 0.5 Se 0.5 )2 crystals are grown by vertical Bridgman-Stockbarger method. Optical properties of deep red LiInSe2, yellowish LiInS2, and orange LiIn(S 0.5 Se 0.5)2 crystals are investigated. Second harmonic generation has been evaluated in LiInSe2 element 6.3 mm long under pumping by CO2 laser, 30 ns pulses, and as high external peak power efficiency as 11.7% has been obtained under optimal conditions.

Development and testing of the lidar gas analyzing complex

Differential Absorption Lidar Complex is designed for field scientific investigations, as well as for teaching Lidar designers and future operators. The Complex consists of two independently working Lidar Systems and the equipment for in situ measurements. Field test results are presented.

ZnGeP 2 crystal: applications for visualization or IR signals

Up-conversion of long, 3-50-μs, pulses imitating input signals of CO2 laser differential absorption lidars was investigated experimentally. Efficiency of 1 to 2% has been acheived when using 1.06-μm Nd:YAG pump emission and 3.9 mm ZnGeP2 crystal that is characterized by absorption coefficient equal to 2.0 cm-1 at this wavelength and 2.5cm-1 at up-converted 0.9548 μm one. When using a silicon avalanche photodiode operating in photon counting mode operation, 450 times increase in signal-to-noise ration can be realized in comparison with dirct detection of the CO2 laser lidar signals by MCT photodiode.

ZnGeP2 crystal is the leader among nonlinear crystals for middle IR

The results of 25-year work on design of middle IR ZnGeP2 crystal growing technology are summed up, so as of the 20-year work on investigation of the parametric frequency converters with this crystal.

Sellmeier equations for LiInS2 and LiInSe2

Disperse properties of biaxial mixed LiIn(Se1-xSx)2, x= 0;0.5; 1, nonlinear crystals are investigated. Most useful Sellmeier equations for parent LiInS2, LiInSe2 and mixed LiIn(Se0.5S0.5)2 crystals are identified from available and original results on disperse properties and experimental phase matiching angles for second harmonic generation. Modernized Sellmeier equations are proposed for parent crystals.

Efficient CO2 frequency doubling with Hg1-xCdxGa2S4

As it is known well, using of frequency doubling in differential absorption CO2 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 HgGa2S4:CdGa2S4→Hg1-xCdxGa2S4, phase-matching and potential efficiencies of second harmonic generation, so as on results of experimental investigation of TEA and mini TEA CO2 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 ZnGeP2 and 5.5 time with AgGaSe2. 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 CO2 laser wavelengths and lower meanings of refractive indexes at fundamental and second harmonic wavelengths. Exploitation parameters of mixed Hg1-xCdxGa2S4 crystal doublers are not worse than parameters of doublers with well-known crystals.

Phase matching and optical properties of LiInS2 nonlinear crystal

Results on investigation of linear and non-linear optical properties, damage threshold and potential efficiencies of biaxial LiInS2 crystal are represented. Transmission range is 0.4 - 12.5 micrometers at the 0.1 level and 0.5 - 11.0 micrometers at the 0.5 level. Typical absorption coefficients are as low as 0,1 - 0,25 cm-1 at the maximum transmission range 1.0 - 8.0 micrometers and 1.1 - 2.3 cm-1 at the CO2 laser wavelengths. Coefficients of second order non-linear susceptibilities are d31 equals 6.2, d32 equals 5.4 and d33 equals 9.8 pm/V, but damage threshold is as high as 120 - 130 MW/sm2 for 36 ns pulses at 9.55 micrometers . The phase-matching is estimated with using of determined Sellmeier coefficients. It is represented in graphic form so as fields of SHG efficiencies. It is shown that LiInS2 can be used in middle IR OPO pumped by Cu-vapor laser, group-velocity phase matching take place in wide spectral range for sum- and difference-frequency generation of visible, near and middle IR lasers including SHG of 3 micrometers Er laser.