title: Coherent terahertz sound amplification and spectral line narrowing in a stark ladder superlattice.
abstract: The bias voltage applied to a weakly coupled n-doped GaAs/AlAs superlattice increases the amplitude of the coherent hypersound oscillations generated by a femtosecond optical pulse. This bias-induced amplitude increase and experimentally observed spectral narrowing of the superlattice phonon mode with a frequency 441 GHz provides the evidence for hypersound amplification by stimulated emission of phonons in a system where the inversion of the electron populations for phonon-assisted transitions exists.
authors.affiliation: School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom.
authors.forename: R P
authors.initials: RP
authors.lastname: Beardsley
authors.forename: A V
authors.initials: AV
authors.lastname: Akimov
authors.forename: M
authors.initials: M
authors.lastname: Henini
authors.forename: A J
authors.initials: AJ
authors.lastname: Kent