title: Picosecond x-ray strain rosette reveals direct laser excitation of coherent transverse acoustic phonons.
abstract: Using a strain-rosette, we demonstrate the existence of transverse strain using time-resolved x-ray diffraction from multiple Bragg reflections in laser-excited bulk gallium arsenide. We find that anisotropic strain is responsible for a considerable fraction of the total lattice motion at early times before thermal equilibrium is achieved. Our measurements are described by a new model where the Poisson ratio drives transverse motion, resulting in the creation of shear waves without the need for an indirect process such as mode conversion at an interface. Using the same excitation geometry with the narrow-gap semiconductor indium antimonide, we detected coherent transverse acoustic oscillations at frequencies of several GHz.
authors.affiliation: Frontier in Extreme Physics, Korea Research Institute of Standards and Science (KRISS), Daejeon 305-600, Korea.
authors.forename: Sooheyong
authors.initials: S
authors.lastname: Lee
authors.affiliation: Department of Physics, DePaul University, Chicago, Illinois 60614, USA.
authors.forename: G Jackson
authors.initials: GJ
authors.lastname: Williams
authors.affiliation: Department of Physics, DePaul University, Chicago, Illinois 60614, USA.
authors.forename: Maria I
authors.initials: MI
authors.lastname: Campana
authors.affiliation: Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors.forename: Donald A
authors.initials: DA
authors.lastname: Walko
authors.affiliation: Department of Physics, DePaul University, Chicago, Illinois 60614, USA.
authors.forename: Eric C
authors.initials: EC
authors.lastname: Landahl