Nonlinear optical coefficients and phase-matching conditions in Sn(2)P(2)S(6)

Phase matching conditions and second and third order nonlinear optical coefficients of Sn2P2S6 crystals are reported. The coefficients for second harmonic generation (SHG) are given at lambda = 1542 nm and 1907 nm at room temperature. The largest coefficients at these wavelengths are d111 = 17+/-1.5pm/V and d111 = 12+/-1.5pm/V, respectively. The third-order subsceptibilities chi(3) 1111 = (17 +/- 6) . 10-20m2/V2 and chi(3) 2222 = (9 +/- 3) . 10-20m2/V2 were determined at lambda = 1907 nm. All measurements were performed by the Maker-Fringe technique. Based on the recently determined refractive indices, we analyze the phase-matching conditions for second harmonic generation, sum- and difference-frequency generation and parametric oscillation at room temperature. Phase-matching curves as a function of wavelength and propagation direction are given. Experimental phase-matched type I SHG at 1907 nm has been demonstrated. The results agree very well with the calculations. It is shown that phase-matched optical parametrical oscillation is possible in the whole transparency range up to 8 microm with an effective nonlinear coefficient deff approximately 4pm/V.