ABSTRACT
Unique holelike small polarons are produced at divalent cation sites by optical excitation at low temperature in single crystals of Sn2P2S6, a monoclinic ferroelectric and photorefractive material. Electron paramagnetic resonance (EPR) is used to observe these self-trapped holes. During an illumination near 25 K with either 442 or 633 nm laser light, photoexcited holes become localized at Sn(2+) (5s(2)) ions and form paramagnetic Sn(3+) (5s(1)) ions. The Sn(3+) ions are thermally stable below 50 K. The principal values of the g matrix are 2.0031, 2.0176, and 2.0273 and the principal values of the (119)Sn hyperfine matrix are 12.828, 12.886, and 13.060 GHz. The large interaction with the (119)Sn (and (117)Sn) nucleus results in a highly asymmetric hyperfine pattern in the EPR spectrum. Weaker hyperfine interactions with two neighboring Sn ions are also observed.
ABSTRACT
Optical rectification is demonstrated in (110)-cut ZnGeP(2) (ZGP) providing broadband terahertz (THz) generation. The source is compared to both GaP and GaAs over a wavelength range of 1150 nm to 1600 nm and peak-intensity range of 0.5 GW/cm(2) to 40 GW/cm(2). ZGP peak-to-peak field amplitude is larger than in the other materials due to either lower nonlinear absorption or larger second-order nonlinearity. This material is well suited for broadband THz generation across a wide range of infrared excitation wavelengths.
