Photo-acoustic terahertz phonon detection and generation within a semiconductor superlattice
Résumé
Currently, the development of compact opto-acoustic transducers able to generate and detect acoustic wave in the terahertz wavelength is an active research subject. Superlattice made with a periodic stacking of AlAs/GaAs layers has shown the ability to be used as high frequency acoustic generators and detectors. The excitation by a femtosecond laser leads to a temporally short strain in the pattern which produces quasi-monochromatic coherent phonons up to a frequency of 1 THz related to the multilayer period (excitation near $q=0$). This superlattice is an effective phonon detector since strain causes a change of reflectivity measured with a probe light. Unfortunately, generation and detection have differents spectrals responses: generation is more efficient around $q=0$, while detection works with $q=2k$ ($k$ is the light vector). Therefore a single superlattice cannot be used to detect and generate the same wave vector. However, theory predicts a rise of $q=0$ detection in case of strong reflection at the interface between superlattice and substrate. To check this possibility we design a sample made of a 17 nm period superlattice embedded in an optical micro-cavity. We will present experiments performed at low temperatures on a sample designed to generate and detect 300 GHz acoustic waves.
Domaines
Acoustique [physics.class-ph]Origine | Fichiers éditeurs autorisés sur une archive ouverte |
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