Increase in the lifetime of a photon and in the efficiency of raman scattering and second-harmonic generation processes in porous silicon carbide

Raman scattering and second-harmonic generation processes in porous layers obtained by the electrochemical etching of polycrystalline silicon carbide, which contain nanocrystals with dimensions from several to hundreds of nanometers, have been studied. It has been found that the efficiencies of Raman scattering and second-harmonic generation in layers of porous silicon carbide increase by several times and more than two orders of magnitude, respectively, compared to the values in the initial sample. The efficiency of transformation to the second harmonic reaches 0.1% at pumping by femtosecond pulses with a wavelength of 1240 nm. The lifetime of a photon in layers of porous silicon carbide has been estimated as more than 2 ps from the measurement of the cross-correlation functions; this value indicates the deceleration of light in this optically inhomogeneous medium owing to multiple scattering. This effect in layers of porous silicon carbide explains the observed increase in the efficiencies of Raman scattering and second-harmonic generation.