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

In this paper, the effect of oxygen content on the linear and nonlinear optical properties of the nanostructured SiOx 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 O2 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 O2 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 O2 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 O2 pressure. The closed aperture Z-scan of SiOx films depicted self-focusing property and the nonlinear refraction coefficient found to be decreasing from 44.2 × 10−5to1.9 × 10−5 cm2/W, with increasing O2 pressure. The significantly large nonlinear third order susceptibility of the order of 10−1–10−3 esu was observed in these films. The SiOx 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. [Display omitted] •Nanostructured SiOx films (x ∼ 0.01–2.1) have been fabricated by PLD.•Shift in stoichiometry from Si-rich to oxygen rich with increasing O2 pressure.•Tunability in band gap from 1.5 to 2.7 eV was obtained with increasing O2 pressure.•Stoichiometry controlled tunable RSA and positive NLR observed under cw He-Ne laser.•SiOx films showed OL effect where threshold increases with increasing oxygen content.