Ternary chalcogenides LiBC2 (B = In, Ga; C = S, Se, Te) for mid-IR nonlinear optics

We review on the growth improvement and optical characterization of a new family of ternary lithium-based chalcogenide crystals of generic formula ${\text{LiB}}^{\text{III}}{\text{C}}_2^{\text{VI}}$ (B = In, Ga; C = S, Se, Te) which displays improved thermo-mechanical properties for mid-IR nonlinear optical applications. Some of these compounds are now produced in sufficiently large size, single-domain quality to allow their implementation in optical parametric oscillators.     

An increased F2-laser damage in ‘wet’ silica glass due to atomic hydrogen: A new hydrogen-related E′-center

A dramatic increase of F₂-laser induced room temperature-stable point defects in ‘wet’ synthetic silica glass occurs when irradiation temperature is lowered to 80 K. Contrary to the predictions based on the established models of defect processes, a large part of defects induced at 80 K remains stable also at the room temperature. The intensities of the laser-induced optical absorption bands of the non-bridging oxygen hole centers (2.0 and 4.8 eV) and E′-centers (5.8 eV) are comparable to those created by neutron irradiation (10¹⁸ n/cm²). A growth of infrared absorption peak at 2237 cm⁻¹ indicates creation of silicon hydride (SiH) groups. A study of irradiation dose dependences and irradiation efficiency at intermediate temperatures (160 K) suggests a novel radiation damage mechanism by insertion of atomic hydrogen in electronically excited Si–O bond. EPR spectra show ${\text{E}}_{\mathrm{\gamma }}^{\prime }$-like centers overlapped by a new type of E′-centers, characterized by a hyperfine splitting of 0.08 mT of the low-field peak in the derivative spectrum. The new E′-center is assigned to a silicon dangling bond, with the Si atom bonded by two bridging oxygens and an OH group (‘E′(OH)’). Similar centers have been previously observed on SiO₂ surfaces.     

Optical properties of amorphous (As0.33S0.67)100−xTex (x = 0, 1, 5 and 10) chalcogenide thin films,photodoped step-by-step with silver

We have analysed in detail the effect of silver-content on the optical properties of Ag-photodoped amorphous (As_0.33S_0.67)_100?xTe_x (with x = 0, 1, 5 and 10 at.%) chalcogenide thin films; the chalcogenide host layers were prepared by vacuum thermal evaporation. Films of composition Ag_y[(As_0.33S_0.67)_100?xTe_x]_100?y, with y ? 18 at.%, were successfully obtained by successively photodissolving about 20- or 40-nm-thick layers of silver. The optical constants (n, k) have been accurately determined by an improved envelope method [J.M. González-Leal, R. Prieto-Alcón, J.A. Angel, D.A. Minkov, E. Márquez, Appl. Opt. 41 (2002) 7300], based on the two envelope curves of the optical-transmission spectrum, obtained at normal incidence. The dispersion of the refractive index of the Ag-photodoped chalcogenide films is analysed in terms of the Wemple–DiDomenico single-effective-oscillator model: $n^2(?\omega )=1-E_{\text{o}}{E}_{\text{d}}/(E_{\text{o}}^2-(?\omega {)}^2)$, where E_o is the single-oscillator energy, and E_d the dispersion energy. We found that the refractive index of the Ag-doped samples strongly increases with the Ag-content, whereas the optical band gap, $E_{\text{g}}^{\text{opt}}$, decreases also notably. For instance, in the particular case of x = 10 at.%, the largest Te-content, $E_{\text{g}}^{\text{opt}}$ decreases from 2.17 down to 1.67 eV. It should also be mentioned that, in the case of the undoped samples, when the Te-concentration increases from zero up to 10 at.%, the value of $E_{\text{g}}^{\text{opt}}$ decreases from 2.49 down to 2.17 eV.