Four‐photon laser spectroscopy of fused quartz and crown glass at 0–60 GHz

Abstract

AbstractThe low wavenumber spectra of fused quartz and crown glass K8 in the range 0.1–2 cm−1 at room temperature were measured by the four‐wave mixing technique. The experimental scheme is based on using both second harmonics of a neodynium‐doped yttrium aluminium garnet (Nd:YAG) pulsed laser and dye laser as a tuning source. The pulse‐to‐pulse deviation of the dye laser frequency is used to obtain the derivative spectra as an additional data source. It was established that the spectra contain a number of narrow (⩽0.1 cm−1) lines. The data could be fitted only by assuming that the Brillouin resonances on longitudinal and transverse sound, as well as the distinct resonances at ∼1.5 cm−1, which can be attributed to hydroxyl (OH) molecular rotations, were involved in the four‐photon scattering process. The fine structure of the Rayleigh wing scattering in fused quartz was observed for the first time. The detected lines, 0.165 cm−1 and 0.26 cm−1 (5.0 and 7.8 GHz, respectively), are attributed to the spheroidal modes ν20 and ν30 of SiO2 spheres with a diameter 880 ± 30 nm. The closely lying eigen modes ν00, ν10 and ν12 are unresolved with a central peak at ± 0.1 cm−1. The 0.4 cm−1 resonance lines in crown glass is attributed to be a manifestation of four‐photon scattering from a second sound phonon. Copyright © 2007 John Wiley & Sons, Ltd.