Optical nonlinearities and thermal lens effect of a-Si:H films investigated by Z-scan technique

Nonlinear optical effects have been studied in hydrogenated amorphous silicon films through the single beam Z-scan technique using a modulated CW laser in the millisecond time-scale regime. In these experiments, the samples were moved through the focal region of a focused gaussian laser beam (λ = 532 nm) while the light transmittance in the far field was measured. The thermal lens effect was observed in the transmittance signal and the time-resolved Z-scan mode could therefore be used to achieve the samples thermal diffusivity (D ∼ 3 x 10-3 cm2/s) and thermal conductivity (K ∼ 5 x 10-3 W/Kcm). The Thermal Lens Model was used to determine the samples temperature coefficient of the optical path length change (ds/dT), and the effective thermal nonlinear refractive index (n2) was estimated by the on-axis non-linear phase shift at focus measurements.