title: First direct measurement of optical phonons in 2D plasma crystals.
abstract: Spectra of phonons with out-of-plane polarization were studied experimentally in a 2D plasma crystal. The dispersion relation was directly measured for the first time using a novel method of particle imaging. The out-of-plane mode was proven to have negative optical dispersion at small wave numbers, comparison with theory showed good agreement. The effect of the plasma wakes on the dispersion relation is briefly discussed.
authors.affiliation: Max-Planck-Institut für Extraterrestrische Physik, 85741 Garching, Germany. lcouedel@mpe.mpg.de
authors.forename: L
authors.initials: L
authors.lastname: Couëdel
authors.forename: V
authors.initials: V
authors.lastname: Nosenko
authors.forename: S K
authors.initials: SK
authors.lastname: Zhdanov
authors.forename: A V
authors.initials: AV
authors.lastname: Ivlev
authors.forename: H M
authors.initials: HM
authors.lastname: Thomas
authors.forename: G E
authors.initials: GE
authors.lastname: Morfill