Phase-Sensitive Optical Detection of Ballistic Phonon Pulses Using Frequency-Modulation Spectroscopy and Persistent Spectral Holes

摘要

Using laser frequency-modulation spectroscopy and persistent spectral holes, time-resolved phase-sensitive probing of ballistic phonons generated by an absorbed Nd:YAG laser pulse is accomplished in the interior of a solid sample. Measurement of the time dependence and sign of a propagating stress-strain field is illustrated using spectral holes in the in-homogeneously broadened 607 nm color center absorption in x-irradiated NaF at liquid-helium temperatures. By examining the dependence of the observed phonon time-of-flight data on the polarization of the probing light, the position within the sample, and the phase of FM detection, an identification of the acoustic polarizations of the propagating phonons may be made. The effects of phonon focusing and mode conversion upon reflection must be taken into account to complete the identification. Along with ability to determine the sign of the acoustic disturbance, this experiment features a strain detection limit of 4 x 10 to the -9th power at a time resolution of 50 ns. Keywords: Optical detection; Ballistic phonons; Frequency modulation spectroscopy; Persistent spectral hole burning. (JHD)