Acoustically induced optical second harmonic generation in hydrogenated amorphous silicon films

Acoustically induced second harmonic generation (AISHG) in hydrogenated amorphous silicon (a-Si: H) films of different morphology has been observed. We have found that with increasing acoustical power, the optical SHG of Gd: YAB laser light (λ = 2.03 μm) increases and reaches its maximum value at an acoustical power density of about 2.10 W cm^-2. With decreasing temperature, the AISHG signal strongly increases below 48 K and correlates well with the temperature behaviour of differential scanning calorimetry indicating near-surface temperature phase transition. The AISHG maxima were observed at acoustical frequencies of 10-11, 14-16, 20-22 and 23-26 kHz. The independently performed measurements of the acoustically induced IR spectra have shown that the origin of the observed phenomenon is the acoustically induced electron-phonon anharmonicity in samples of different morphology.