The third order nonlinear optical characteristics of amorphous vanadium oxide thin film

We studied the nonlinear absorptive characteristics (saturation intensity threshold and effective nonlinear absorption coefficients) and nonlinear refraction in a 50-nm-thick VO _x thin amorphous film prepared by pulsed DC magnetron reactive sputtering. The absorptive and refractive nonlinearities were investigated by pump–probe and Z-scan techniques. The closed-aperture Z-scan results reveal self-defocussing characteristics of the amorphous VO _x thin film for both nanosecond and picosecond pulse durations. Experimental results show that a phase transition does not occur in the range of intensities used for the experiments and the investigated sample can be treated as an amorphous semiconductor structure. The open-aperture Z-scan curves with nanosecond pulses exhibit saturable absorption for all input intensities. On the other hand, the open-aperture Z-scan curves with picosecond pulses exhibit nonlinear absorption/saturable absorption for low/high input intensities, respectively. Saturation intensity thresholds were found to be 15.3 MW/cm² for 4-ns pulse duration and 586 MW/cm² for 65-ps pulse duration.