Optical, vibrational, thermal, electrical, damage and phase-matching properties of lithium thioindate

Lithium thioindate (LiInS$_{2}$) is a new nonlinear chalcogenide biaxial material transparent from 0.4 to 12 $\mu$m, that has been successfully grown in large sizes and good optical quality. We report on new physical properties that are relevant for laser and nonlinear optics applications. With respect to AgGaS(e)$_2$ ternary chalcopyrite materials, LiInS$_{2}$ displays a nearly-isotropic thermal expansion behavior, a 5-times larger thermal conductivity associated with high optical damage thresholds, and an extremely low intensity-dependent absorption allowing direct high-power downconversion from the near-IR to the deep mid-IR. Continuous-wave difference-frequency generation (5-11$\mu$m) of Ti:sapphire laser sources is reported for the first time.Comment: 27 pages, 21 figures. Replaces the previous preprint (physics/0307082) with the final version as it will be published in J. Opt. Soc. Am. B 21(11) (Nov. 2004 issue

Raman detection of the superconducting gap in Ba-Y-Cu-O superconductors

We have utilized an iodine absorption cell to enable detailed Raman studies at low frequency (down to 15 cm-1) in a thin film of the high-temperature superconductor Ba2YCu3O7. Subtraction of spectra just above and well into the superconducting phase reveals a weak broad feature (maximum near 400 cm-1, half width at half maximum approximately 250 cm-1), which we tentatively interpret as due to scattering near the superconducting gap. The large width of the feature may be partially related to smearing of the transition, or to gap anisotropy. Its onset near 200 cm-1 suggests an energy gap 2Δ near 25 meV. Assuming that the surface region probed in the scattering has the same Tc as that measured for the overall film (onset 85 K), we obtain the ratio r=2Δ/kBTc=3.4±1.5, consistent with the BCS weak-coupling value of 3.5