title: Observing backfolded and unfolded acoustic phonons by broadband optical light scattering.
abstract: We use broadband time domain Brillouin scattering to observe coherently generated phonon modes in bulk and nanolayered samples. We transform the measured transients into a frequency-wavevector diagram and compare the resulting dispersion relations to calculations. The detected oscillation amplitude depends on the occupation of phonon modes induced by the pump pulse. For nanolayered samples with an appropriately large period, the whole wavevector range of the Brillouin zone becomes observable by broadband optical light scattering. The backfolded modes vanish, when the excitation has passed the nanolayers and propagates through the substrate underneath.
authors.affiliation: Institut für Physik & Astronomie, Universität Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany.
authors.forename: L
authors.initials: L
authors.lastname: Maerten
authors.affiliation: Institut für Physik & Astronomie, Universität Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Bojahr
authors.affiliation: Institut für Physik & Astronomie, Universität Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany; Helmholtz-Zentrum-Berlin für Energie und Materialforschung, Wilhelm-Conrad-Röntgen Campus, BESSY II, Albert-Einstein-Str. 15, 12489 Berlin, Germany. Electronic address: bargheer@uni-potsdam.de.
authors.forename: M
authors.initials: M
authors.lastname: Bargheer
keywords: Broadband detection; Phonon backfolding; Phonon dispersion; Superlattice; Time resolved Brillouin scattering