Structure and nonlinear optical properties of TeO2–WO3–PbO thin film glasses

ABSTRACT: Lead tungsten tellurite thin film glasses have been produced by pulsed laser deposition in a broad TeO 2 compositional range (50-85 mol%). Films present high transparency with an optical band gap E g = 3.3-3.4 eV, large refractive index ( n > 2) and reduced absorption ( k < 10 -4 ) in the visible and near infrared ranges, whereas their nonlinear optical response ( ∣χ (3) ∣ ) is found to be ≥ 10 -12 esu at 1.3 μm. The dependence of n , E g and ∣χ (3) ∣ with film composition is analyzed and compared with the values determined for the parent bulk glasses. ∣χ (3) ∣ increases as the TeO 2 content in the film glasses decreases, while it remains constant for bulk glasses. This behaviour is analyzed in the frame of Line’s model and correlated to the structural differences between bulk and film glasses. In the case of bulk glasses, X-ray absorption spectroscopy results at the W L 3 and L 1 -edges clearly indicate the presence of W 6+ ions in a distorted octahedral coordination, with the coordination environment and W-O bond distance remaining unchanged regardless of the WO 3 content. Raman analysis suggests that films have a structure close to that of bulk glasses, with a moderate WO 3 and PbO enrichment, and a relative increase of the non-bridging oxygen fraction that are proposed to be responsible for the observed increase of ∣χ (3) ∣ in the films.