ИСТИНА

Arrays of silicon nanowires (SiNWs) of about 100 nm in diameter formed by metal- assisted chemical etching of crystalline silicon (c-Si) substrates were studied with the help of third-harmonic (TH) generation technique. The SiNW arrays demonstrate strong scattering, which results in enhanced photon lifetime in them as it was supported by measurements of the cross-correlation function for femtosecond pulses scattered by the SiNW arrays. This effect results in an order of magnitude growth of TH generation efficiency compared to the signals for c-Si. Using (110) oriented c-Si substrate we managed to make well-oriented tilted SiNWs demonstrating strongly anisotropy of the TH signal. Numerical simulations of circularly polarized light scattering by a single SiNW and a group of 13 SiNWs used as a geometrical approximation of the real SiNW array indicate maintenance of helical modes in SiNWs for the light incident at an oblique angle to their axis. This result found its experimental confirmation in an experiment on the TH generation pumped by femtosecond laser pulses at 1250 nm demonstrated significant difference in the TH signals for cases of left- and right-handed circularly polarized fundamental radiation. The effect was detected for oblique (60°) light incidence on SiNWs, whereas for the laser radiation propagating along the SiNWs or perpendicularly to them TH signal did not depend on the pump radiation photon helicity sign. This fact is a manifestation of photon spin Hall effect. Thus, geometrical structure of the SiNW arrays, photon lifetime and local field in them strongly effects on efficiency and polarization properties of the third-harmonic generation.