Abstract

We have detected using superconducting bolometers the phonons generated by ultra-fast pulsed laser excitation of gallium arsenide/aluminium arsenide superlattice structures. In addition to the enhancement of the longitudinal acoustic (LA) phonon previously reported, we observe an enhancement of the signal due to ballistic transverse acoustic (TA) phonons when the condition for coherent phonon generation is satisfied, that is, the pump photon energy is equal to the exciton energy in the quantum wells. TA modes are not Raman active in (001) GaAs, therefore impulsively stimulated Raman scattering (ISRS), believed to be the mechanism for generation of LA modes, is unlikely to be responsible for the TA emission. We consider other processes which might be responsible for generation of the TA phonons.

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