Radiant energy – Radiant energy generation and sources
Reexamination Certificate
2003-09-26
2004-12-07
Wells, Nikita (Department: 2881)
Radiant energy
Radiant energy generation and sources
C250S363010, C250S36100C, C250S362000, C250S336100, C385S129000, C385S132000
Reexamination Certificate
active
06828575
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to the field of Cherenkov radiation, and in particular to using photonic crystals as a medium to exhibit anomalous Cherenkov radiation.
Cherenkov radiation (CR) is the coherent electromagnetic response of a medium driven by the swift passage of a charged particle. It is thus an effect strongly dependent on the medium dispersion. In a uniform, isotropic medium with frequency-independent permittivity ∈ and permeability &mgr;, the condition for CR is well-known, where the velocity of the particle v must exceed the phase velocity of the medium &ugr;
ph
=c/√{square root over (∈&mgr;)}. For a dispersive medium, such as a nonmagnetic material with a Lorentz-form dielectric response ∈(&ohgr;), &ugr;
ph
(&ohgr;)=c/√{square root over (∈(&ohgr;))}, is a function of frequency &ohgr;. Because ∈(&ohgr;) can reach arbitrarily high values near a resonance, it was long recognized that CR in a dispersive medium can happen for small charge velocities, e.g., &ugr;<&ugr;
ph
(0). The sub-threshold CR in a material near its phonon-polariton resonance was disclosed in
Cherenkov Radiation at Speeds Below the Light Threshold: Phonon
-
Assisted Phase Matching
, by T. E. Stevens, J. K. Wahlstrand, J. Kuhl, and R. Merlin, SCIENCE, vol. 291, No. 5504 (26 Jan. 2001).
On the other hand, it was conjectured that there could exist another class of materials which have both ∈ and &mgr; being negative, henceforth referred to as “negative index materials.” The properties of such materials were disclosed in
The Electrodynamics of Substances with Simultaneously Negative Values of ∈ and &mgr;,
by V. G. Veselago, SOVIET PHYSICS USPEKHI, vol. 10, No. 4 (January-February 1968). It was suggested that a negative index material would reverse many of the well-known laws of optics. In particular, CR effect is predicted to be reversed, i.e., a fast-moving charge in a negative index medium should radiate in the direction opposite to that of its velocity.
A further possibility exists when the charged particle travels near a periodic structure, where simple Bragg scattering can give rise to radiation without any velocity threshold. This phenomenon (the Smith-Purcell effect) was disclosed in
Visible Light from Localized Surface Charges Moving across a Grating
, by S. J. Smith and P. M. Purcell, PHYSICAL REVIEW, vol. 92, No. 4 (15 Nov. 1953). The radiation due to traveling charged particles has since been studied in one-dimensionally periodic multilayer stacks in
Cerenkov Radiation in Inhomogeneous Periodic Media,
by K. F. Casey, C. Yeh, and Z. A. Kaprielian, PHYSICAL REVIEW, vol. 140, No. 3B (8 Nov. 1965), and near the surface of dielectric structures in
Interactions of Radiation and Fast Electrons with Clusters of Dielectrics: A Multiple Scattering Approach
, by F. J. Garcia de Abajo, PHYSICAL REVIEW LETTERS, vol. 82, No. 13 (29 Mar. 1999).
SUMMARY OF THE INVENTION
According to one aspect of the invention, there is provided a system for exhibiting Cherenkov radiation. The system includes a beam of traveling charged particles. A photonic crystal structure receives the beam of charged particles. The charged particles move in the photonic crystal structure so that CR is produced at all velocities without requiring resonances in the effective material constants of said photonic crystal structure.
According to another aspect of the invention, there is provided a method of exhibiting Cherenkov radiation. The method includes providing a beam of traveling charged particles. Also, the method includes providing a photonic crystal structure that receives the beam of charged particles. The charged particles move in the photonic crystal structure so that Cherenkov radiation is produced at all velocities without requiring resonances in the effective material constants of said photonic crystal structure.
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“The Electrodynamics of substances with simultaneously negative values of ∈ and &mgr;, ” Veselago.Soviet Physics. Jan-Feb. 1968. vol. 10, No. 4.
“Cherenkov Radiation at Speeds Below the Light Threshold: Phonon-Assisted Phase Matching,” Stevens et al.Science. Jan 2001. vol. 291.
“Visible Light from Localized Surface Charges Moving Across a Grating,” Smith et al.Letters to the Editor. Sep. 1953.
“Interaction of Radiation and Fast Electrons with clusters of Dielectrics: A Multiple Scattering Approach,” Abajo.Physical Review Letters. Mar. 1999. vol. 82, No. 13.
“Cerenkov Radiation in Inhomogeneous Periodic Media,” Casey et al.Physical Review. Nov. 1965. vol. 140, No. 3B.
“Slow Group Velocity and Cherenkov Radiation,”Physical Review Letters. Aug. 2001. vol. 87, No. 6.
“Cerenkov Radiation in Photonic Crystals,” Luo et al.Science. Jan. 2003. vol. 299.
“Smith-Purcell radiation from metallic and dielectric photonic crystals,” Ohtaka. Technical Digest. Cleo/Pacific Rim 2001. 4thPacific Rim Conference on Lasers and Electo-optics. Jul. 2001. p. I-272-3.
Ibanescu Mihai
Joannopoulos John D.
Johnson Steven G.
Luo Chiyan
Gauthier & Connors LLP
Massachusetts Institute of Technology
Wells Nikita
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