title: Coherent control of pulsed X-ray beams.
abstract: Synchrotrons produce continuous trains of closely spaced X-ray pulses. Application of such sources to the study of atomic-scale motion requires efficient modulation of these beams on timescales ranging from nanoseconds to femtoseconds. However, ultrafast X-ray modulators are not generally available. Here we report efficient subnanosecond coherent switching of synchrotron beams by using acoustic pulses in a crystal to modulate the anomalous low-loss transmission of X-ray pulses. The acoustic excitation transfers energy between two X-ray beams in a time shorter than the synchrotron pulse width of about 100 ps. Gigahertz modulation of the diffracted X-rays is also observed. We report different geometric arrangements, such as a switch based on the collision of two counter-propagating acoustic pulses: this doubles the X-ray modulation frequency, and also provides a means of observing a localized transient strain inside an opaque material. We expect that these techniques could be scaled to produce subpicosecond pulses, through laser-generated coherent optical phonon modulation of X-ray diffraction in crystals. Such ultrafast capabilities have been demonstrated thus far only in laser-generated X-ray sources, or through the use of X-ray streak cameras.
authors.affiliation: Department of Physics and FOCUS Center, University of Michigan, Ann Arbor, Michigan 48109, USA. mattydee@umich.edu
authors.forename: M F
authors.initials: MF
authors.lastname: DeCamp
authors.forename: D A
authors.initials: DA
authors.lastname: Reis
authors.forename: P H
authors.initials: PH
authors.lastname: Bucksbaum
authors.forename: B
authors.initials: B
authors.lastname: Adams
authors.forename: J M
authors.initials: JM
authors.lastname: Caraher
authors.forename: R
authors.initials: R
authors.lastname: Clarke
authors.forename: C W
authors.initials: CW
authors.lastname: Conover
authors.forename: E M
authors.initials: EM
authors.lastname: Dufresne
authors.forename: R
authors.initials: R
authors.lastname: Merlin
authors.forename: V
authors.initials: V
authors.lastname: Stoica
authors.forename: J K
authors.initials: JK
authors.lastname: Wahlstrand