title: Cherenkov radiation at speeds below the light threshold: phonon-assisted phase matching.
abstract: Charged particles traveling through matter at speeds larger than the phase velocity of light in the medium emit Cherenkov radiation. Calculations reveal that a given angle of the radiation conical wavefront is associated with two velocities, one above and one below a certain speed threshold. Emission at subluminal but not superluminal speeds is predicted and verified experimentally for relativistic dipoles generated with an optical method based on subpicosecond pulses moving in a nonlinear medium. The dipolar Cherenkov field, in the range of infrared-active phonons, is identical to that of phonon polaritons produced by impulsive laser excitation.
authors.affiliation: The Harrison M. Randall Laboratory of Physics, University of Michigan, Ann Arbor, MI 48109-1120, USA.
authors.forename: T E
authors.initials: TE
authors.lastname: Stevens
authors.forename: J K
authors.initials: JK
authors.lastname: Wahlstrand
authors.forename: J
authors.initials: J
authors.lastname: Kuhl
authors.forename: R
authors.initials: R
authors.lastname: Merlin