Observation of Thermal Phonon Resonance in Cylindrical Microcavities

概要

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Brillouin scattering measurements were made in small capillary tubes filled with water with 1450 μm and 920 μm in inner diameters. Hyper-resolution spectroscopy using an optical beating technique revealed thermal phonon resonance in the cavity around 8 MHz and 30 MHz. The observed spectra have a complicated structure with periodical main peaks and other subpeaks accompanying each main peak. The resonance frequencies of the cylindrical phonon modes were theoretically calculated and given through a series of n-th order Bessel functions. Frequencies of the fundamental (n = 0, 1) modes were in good agreement with those of the observed main peaks, and the subpeaks were associated with higher modes with n ≥ 2. The mode assignment was successful. As the frequency increased, all the sub-peaks gathered towards the relevant main peak and were degenerated. This phenomenon was applied to measure the phonon velocity of liquid confined in a small cavity. Measurement was made for water over a temperature range from 20 to 28℃, and the result demonstrated a high sensitivity for detecting velocity changes smaller than 0.1 %.
社団法人応用物理学会の論文
1999-08-15