Stoichiometry-dependent linear and nonlinear optical properties of PLD SiO x thin films

Abstract

Abstract In this paper, the effect of oxygen content on the linear and nonlinear optical properties of the nanostructured SiO x thin films on fused silica is reported. The films were fabricated by Pulsed Laser Deposition technique at a substrate temperature of 400 °C in presence of O 2 pressure, ranging from 10 −4 to 0.5 mbar. X-Ray Diffraction spectra confirmed the formation of polycrystalline Si. Energy Dispersive X-Ray spectra showed the increase in oxygen content with increasing O 2 pressure. Linear absorption coefficients and refractive index were estimated from UV–Vis–NIR transmission spectra. Static refractive index of the films was found to vary from 3.57 to 1.57, with the increase in O 2 pressure. The open Z -scan spectrum of the thin films, using He-Ne laser, exhibited strong reverse saturation absorption and the non linear absorption coefficient measured from it was observed to be decreasing from 21.4 to 2.0 cm/W, with increase in the O 2 pressure. The closed aperture Z -scan of SiO x films depicted self-focusing property and the nonlinear refraction coefficient found to be decreasing from 44.2 × 10 −5 to1.9 × 10 −5 cm 2 /W, with increasing O 2 pressure. The significantly large nonlinear third order susceptibility of the order of 10 −1 –10 −3 esu was observed in these films. The SiO x films except the one containing maximum oxygen content exhibited optical limiting, where limiting threshold increases with increasing transparency which in turn is modulated by oxygen content.