Abstract
We performed time-resolved reflectivity measurements and characterized the time-varying oscillations of longitudinal acoustic phonons in InGaAsP multiple quantum wells (MQWs) by asynchronous optical sampling with Er-doped fiber lasers. Oscillations of longitudinal acoustic phonons ranging from a few tens to a few hundred gigahertz were observed, which were induced by forward and backward Raman scattering in Brillouin and first zone-folded acoustic phonon modes. To investigate the dynamics of each phonon mode for various pump-probe time delays, we analyzed the experimental data with a continuous wavelet transformation (CWT) and a subsequent modified inverse CWT. For high-frequency oscillations, we observed the oscillatory profile with beats and identified the contribution of each phonon mode. For low-frequency oscillations, a series of dissipations of phonon wave packets from each QW to the InP substrate was deduced from the analyzed data. These results suggest that our analysis method is useful for investigating the dynamics of acoustic phonons.
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