skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Superradiant Spin-Flip Radiative Emission of a Spin-Polarized Free-Electron Beam

Abstract

Radiative emission from the magnetic moments of the spins of an electron beam has never been observed directly, because it is fundamentally much weaker than the electric charge emission. We show that the detectivity of spin-flip and combined spin-flip-cyclotron-resonance-emission radiation can be substantially enhanced by operating with ultrashort spin-polarized electron beam bunches under conditions of superradiant (coherent) emission. The proposed superradiant spin-flip radiative emission scheme can be used for noninvasive diagnostics of polarized electron or positron beams. Such beams are of relevance in important scattering experiments off nucleons in nuclear physics and off magnetic targets in condensed matter physics.

Authors:
 [1]
  1. Faculty of Engineering, Department of Physical Electronics, Tel-Aviv University, Ramat-Aviv 69978, Tel-Aviv (Israel)
Publication Date:
OSTI Identifier:
20777119
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 96; Journal Issue: 12; Other Information: DOI: 10.1103/PhysRevLett.96.124801; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; BEAM BUNCHING; CYCLOTRON RESONANCE; ELECTRIC CHARGES; ELECTRODYNAMICS; ELECTRON BEAMS; ELECTRONS; MAGNETIC MOMENTS; NUCLEONS; POSITRON BEAMS; SCATTERING; SPIN; SPIN FLIP; SPIN ORIENTATION; SUPERRADIANCE

Citation Formats

Gover, A. Superradiant Spin-Flip Radiative Emission of a Spin-Polarized Free-Electron Beam. United States: N. p., 2006. Web. doi:10.1103/PhysRevLett.96.124801.
Gover, A. Superradiant Spin-Flip Radiative Emission of a Spin-Polarized Free-Electron Beam. United States. doi:10.1103/PhysRevLett.96.124801.
Gover, A. Fri . "Superradiant Spin-Flip Radiative Emission of a Spin-Polarized Free-Electron Beam". United States. doi:10.1103/PhysRevLett.96.124801.
@article{osti_20777119,
title = {Superradiant Spin-Flip Radiative Emission of a Spin-Polarized Free-Electron Beam},
author = {Gover, A.},
abstractNote = {Radiative emission from the magnetic moments of the spins of an electron beam has never been observed directly, because it is fundamentally much weaker than the electric charge emission. We show that the detectivity of spin-flip and combined spin-flip-cyclotron-resonance-emission radiation can be substantially enhanced by operating with ultrashort spin-polarized electron beam bunches under conditions of superradiant (coherent) emission. The proposed superradiant spin-flip radiative emission scheme can be used for noninvasive diagnostics of polarized electron or positron beams. Such beams are of relevance in important scattering experiments off nucleons in nuclear physics and off magnetic targets in condensed matter physics.},
doi = {10.1103/PhysRevLett.96.124801},
journal = {Physical Review Letters},
number = 12,
volume = 96,
place = {United States},
year = {Fri Mar 31 00:00:00 EST 2006},
month = {Fri Mar 31 00:00:00 EST 2006}
}
  • In this paper, the authors report on a new regime of free electron laser operation using a helical wiggler field and a reversed axial guide magnetic field. The orientation of the axial field is such as to oppose the electron rotation imparted by the helical field. The 33.3 GHz free electron laser amplifier is driven by a mildly relativistic electron beam (750 kV, 300 A, 30 ns) and generates 61 MW of radiation with a 27% conversion efficiency. The results are compared with those obtained when the axial guide field is in its conventional orientation, where considerable loss of powermore » and efficiency is observed.« less
  • For the first time superradiant emission from an electron-beam-excited dye vapor has been observed. Temporal and spectral characteristics are described that confirm the presence of stimulated emission. The wavelength integrated net gain of an optimized POPOP dye vapor--buffer gas mixture is found to be 0.17 cm/sup -1/ at 1 Torr and 4 atm argon pressures for an absorbed power input of 40 MW into an active volume of 10 cm/sup 3/. Under these conditions an estimate of the conversion efficiency from electronic energy to coherent light yields 5%. These results suggest that an efficient tunable electronically pumped dye vapor lasermore » system is feasible.« less
  • The transverse relaxation of the muon spin in muonium due to electron spin exchange with a polarized spin-1/2 medium is investigated. Stochastic calculations, which assume that spin exchange is a Poisson process, are carried out for the case where the electron spin polarization of the medium is on the same axis as the applied field. Two precession signals of muonium observed in intermediate fields ([ital B][gt]30 G) are shown to have different relaxation rates which depend on the polarization of the medium. Furthermore, the precession frequencies are shifted by an amount which depends on the spin-nonflip rate. From the twomore » relaxation rates and the frequency shift in intermediate fields, one can determine (i) the encounter rate of muonium and the paramagnetic species, (ii) the polarization of the medium, and most importantly (iii) the quantum-mechanical phase shift (and its sign) associated with the potential energy difference between electron singlet and triplet encounters. Effects of spin-nonflip collisions on spin dynamics are discussed for non-Poisson as well as Poisson processes. In unpolarized media, the time evolution of the muon spin in muonium is not influenced by spin-nonflip collisions, [ital if] [ital the] [ital collision] [ital process] [ital is] [ital Poissonian]. This seemingly obvious statement is not true anymore in non-Poissonian processes, i.e., it is necessary to specify both spin-flip and spin-nonflip rates to fully characterize spin dynamics.« less
  • The energy-resolved spin polarization P of secondary electrons from Ni(110) has been measured with high energy resolution. At the lowest kinetic energy P reaches a maximum of (17 +- 2)% which is significantly higher than the mean conduction-band polarization (5.5%). Within about 3 eV towards higher kinetic energy the spin polarization decreases to about 8% and displays pronounced structures at higher energies. Spin-dependent electron-hole pair excitations are suggested to be responsible for the observed spin polarization. .ID LW2044 .PG 74 77
  • The exchange interaction and the spin-orbit interaction are observed to cause a spin dependence of the absorption of a polarized electron beam in the amorphous ferromagnet Ni/sub 40/Fe/sub 40/B/sub 20/ and a W(100) single crystal respectively. The enhancement of the spin dependence, near the energy where the secondary electron yield is unity, is shown to provide a simple efficient detector of spin polarization.