Second-Harmonic and Sum-Freqency Generation in CdGeAs 2
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Department of Computer Science
,
Keio University,
Hiyoshi 3-14-1, Kohoku-ku, Yokohama, Japan **Second Research Center, Japan Defense Agency Ikejiri 1-2-24, Setagaya, Tokyo, Japan Abstract CdGeAs 2 has been found to be phase-matchable for type-2 SHG down to 2.833 uz m and type-2(b) SFG between the fundamental and second harmonic of a CO 2 laser down to l0.4406~t m at 20.0°C. The Sellmeier's equations and the thermo-optic dispersion formula which reproduce well the phasematching properties of SHG and direct FHG of the CO 2 lasers at 77K are presented together with the absolute value of the nonlinear optical constant.
Recent progress in the growth of CdGeAs 21 ° )'(2• has generated renewed interest in its potential for high power harmonic generation of a CO 2 laser and
parametric oscillation in the mid to far IR when pumped by the solid state lasers. However, since the phase-matching conditions of this material thus far reported in the literature show large scatters from those predicted by the Sellmeier's equations of Kildal and Mikkelsen( 3 • and Bhar( 4•, we remeasured the phase-matching properties of this compound for type-2 SH-G and SFG in the 2.65-5.30 ii m range and found that this material is 90° phase matchable for type-2 SHG of the 5.670 ji m and type-2(b) SFG between the fundamental and second harmonic of a CO 2 laser at 10.4406,u m at 20.0°C. Here, we report some new experimental results on the IR frequency conversion in CdGeAs 2 along with the improved Sellmeier's equations and the thermo-optic dispersion formula which reproduce well the phase-matching
475 Mat. Res. Soc. Symp. Proc. Vol. 484 © 1998 Materials Research Society
conditions for SHG(5 ) and direct FHG(6) of the CO 2 laser observed at 100 and 77K. In addition, the absolute value of the nonlinear optical constant is presented. The CdGeAs 2 crystals used in this experiment were supplied by the Eksma,Inc. in Lithuania and were fabricated at ( 0 =90' , 4 =45' ) and ( 0 =49.1'
6 , -1=45° ). The dimensions of these two crystals were 8 X 8 XK
3
mm . The short and long cutoff wavelengths are 2.45 and 18.1 11m. Using a Ho:YLF laser pumped AgGaSe 2 OPO and the CO 2 laser as the pump source, we first measured the phase-matching angles for type-2 SHG in the short and long wavelength branches at 20.0'C. The experimental results were found to be in excellent agreement with the values calculated with the following Sellmeier's equations: 2.1603 2
n. =12.4008+
ne 2=13.0079+
-
2
3.2613 2-
0.00133 ;L 2
- 0.00126*2
2.8382
where X is in micrometers. The shortest SHG and SFG wavelengths generated in this experiment were 2.833 and 3.4802 kt m. Although the data points of Boyd et al(7 ) for type-1 and type-2 SHG of 10.5910gt m are
"-2.5' larger than our measured and calculated values of 0 eeo=32.6° and 0 0,°=49.3'
owing to the smaller birefringence of the BTLs crystals, our
index formula reproduce well the experimental results of the-Stanford and MIT groups. In addition, this formula correctly reproduces the phasematching conditions for type-2 DFG
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