Acoustically induced optical second harmonic generation in hydrogenated amorphous silicon films

Abstract

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.