Linear and nonlinear properties of laser-ablated Si films in the 9.0-9.6-μm wavelength region

The linear and nonlinear properties of Si thin films upon Si wafers made by the use of laser ablation are presented. The linear absorption of the films clearly showed a peak at 9.8 μm (1020 cm^-1), whereas the peak at 9.04 μm (1070 cm^-1) from the asymmetric Si-O-Si vibration mode was absent. Raman spectroscopy data show a typical 4-cm^-1 downshift with respect to the Si line. The nonlinear measurements were performed with a tunable free-electron laser. The nonlinear absorption at λ = 9.2 μm was measured to be approximately 2, 25, and 5 times larger than the nonlinear absorption at λ = 9.0 μm, λ = 9.4 μm, and λ = 9.6 μm, respectively.