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Cherenkov Radiation at Speeds Below the Light Threshold: Phonon-Assisted Phase Matching

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Science  26 Jan 2001:
Vol. 291, Issue 5504, pp. 627-630
DOI: 10.1126/science.291.5504.627

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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.

  • * Present address: Veridian ERIM International, Post Office Box 134008, Ann Arbor, MI 48113–4008, USA.

  • To whom correspondence should be addressed. E-mail: merlin{at}umich.edu

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