Monochromatic transverse-polarized phonons from femtosecond pulsed optical excitation of a GaAs/AlAs superlattice

摘要

We have generated pulses of ～0.5 THz, monochromatic transverse-polarized acoustic (TA) phonons by resonant excitation of a (001) GaAs/AlAs superlattice (SL) structure using femtosecond optical pulses. The phonons were detected using superconducting bolometers. Spectral resolution was obtained by using the filter effect of the frequency-dependent phonon scattering in the GaAs substrate and also using a second superlattice as a notch filter placed between the generator and bolometer. We propose that the detected TA phonons are due to the leakage of optically excited coherent SL modes into propagating phonons. We discuss various mechanisms by which TA phonons, which are not Raman active in (001) GaAs, may couple with the optical pump pulse.