Enhancement of two-photon absorption in anisotropic mesoporous silicon

In experiments on nonlinear‐optical transmission of picosecond laser pulses at the wavelength of 1.064 μm threeorder‐of‐magnitude enhancement of the photoinduced absorption in optically anisotropic mesoporous silicon films compared to crystalline silicon (c‐Si) was found. The effect is not sensitive to the polarization of the laser radiation and it saturates at laser peak intensities about 5 MW/cm2. Higher laser intensity results in the polarization‐sensitive photoinduced absorption, which is merely one‐order‐of‐magnitude more effective than in c‐Si. These efficient nonlinear‐optical responses can be attributed to the resonant excitation of the defect states in the direct gap of silicon and local‐field enhancement in the mesoporous films. (© 2008 by Astro Ltd., Published exclusively by WILEY‐VCH Verlag GmbH & Co. KGaA)