Enhanced and tunable nonlinear optical responses of nitrogen-doped nickel oxide induced by femtosecond laser excitation

Abstract In this work, we report the impact of nitrogen (N) doping in nickel oxide films on nonlinear optical responses (NORs) utilizing 532 nm, 330 fs laser pulses with both linear and radial polarization states. The pristine and N-doped NiO films are grown through radio frequency magnetron sputtering technique and further characterized by AFM, UV–Vis transmittance spectra and XPS. The experimental results demonstrate that NORs, including reverse saturable absorption and optical Kerr refraction, of the as-prepared NiO films along with their optical power limiting (OPL) are intimately related to the N doping and the laser polarization patterns. More specifically, both the NORs and OPL increase scalingly with the doping concentration under the linearly polarized laser excitation. The strongest optical nonlinear absorption coefficient, optical nonlinear refraction index and OPL efficiency are in turn determined to be 4.55 × 10−7 m/W, 6.5 × 10−16 m2/W and 50% for the heaviest N-implanted NiO film. In a sharp contrast, for the raidally polarized beam impinging onto the pristine and doped NiO films, the NORs and OPL initially drop off and then strengthen together as the increases of N-implanted content. Such enhanced and tunable NORs are due to the fact that the involvement of doping state gives rise to promoted optical transitions originating from the narrowing of band gap, as well as the use of ultrafast vectorial laser induces anisotropic nonlinearity and intricate light-matter interplay. Our results will open a new perspective to develop optical power limiter and ultrafast photonic devices.