Optical Properties of a New Nonlinear Optical Material: Tl_3AsSe_3

We report on the synthesis and the measurement of the properties of large single crystals of a new synthetic nonlinear optical material of the sulfosalt type, Tl(3)AsSe(3). The crystal space group is R3m; the refractive indices range from 3.14 to 3.44 with n(0) - n(e) = 0.18 (negative uniaxial), and the material is transparent from 1.26 microm to beyond 17 microm. The nonlinear optical susceptibilities are of the order of three times those of Ag(3)AsS(3) (proustite), in reasonable agreement with Miller's rule, and the measured phase-match angle for frequency doubling of the CO(2) laser output (10.6 microm) is theta(m) = 22 +/- 2 degrees . Calculations of tuning curves for parametric oscillation indicate the possibility of angle tuning over the entire transparency range of the crystal; pumping at 2.06 microm (Ho(3+)-doped YAG or SOAP) appears to be a promising technique for obtaining efficient tunable parametric oscillation in the 3-5-microm region.