We present data on the linear (transmission, index of refraction) and nonlinear (second-order susceptibility) optical properties of the quaternary semiconductor AgGaGe<sub>5</sub>Se<sub>12</sub> with orthorhombic symmetry—a solid solution in the Ag<sub><i>x</i></sub>Ga<sub><i>x</i></sub>Ge<sub>1−<i>x</i></sub>Se<sub>2</sub> system with <i>x</i> = 0.17. The nonlinear coefficients are estimated from phase-matched second-harmonic generation near 3 μm. After numerical analysis of the phase-matching configurations for three-wave nonlinear interactions, the first experimental results on difference-frequency mixing, producing tunable (4–7.5-μm) femtosecond pulses at a 1-kHz repetition rate, are described. The pulses of only five optical cycles (FWHM = 84 fs) are generated near 5 μm with energy of 0.5 μJ. Because of its higher damage threshold, larger birefringence and bandgap, and greater variety of phase-matching schemes, AgGaGe<sub>5</sub>Se<sub>12</sub> could become an alternative to AgGaS<sub>2</sub> and AgGaSe<sub>2</sub>, more widely used in high-power and specific applications.
© 2004 Optical Society of America
V. Petrov, F. Noack, V. Badikov, G. Shevyrdyaeva, V. Panyutin, and V. Chizhikov, "Phase-Matching and Femtosecond Difference-Frequency Generation in the Quaternary Semiconductor AgGaGe5Se12," Appl. Opt. 43, 4590-4597 (2004)