2C07

Electromagnetic Wave Propagation Below Cutoff

P. Sprangle and E. Esarey, Plasma Physics Division,

Naval Reseach Laboratory, Washington, DC B. Hafizi

ICARUS Research, Inc., Bethesda, MD S.E. Harris

Stanford University, Stanford, CA

A small amplitude electromagnetic wave can propagate in a plasma below cutoff in the presence of a high frequency large amplitude wave. This is referred to electromagnetically induced transparency (EIT).' We extend the analysis of EIT to include relativistic and collisional effects as well as density gradients. We show that the small amplitude wave is unstable in certain parameter regimes. Well above cutoff the instability goes over to the usual backward Raman instability. In addition, the propagation of a large amplitude wave in an inhomogeneous plasma and its penetration beyond the critical surface is analyzed.

photons by a colliding probe laser pulse, without requiring complex structures to terminate the interaction. In this process, the photon energy scales as

h v ~ 4 - y O A l hc 2 4 , A0

where & is the laser wavelength (pump and probe), yo is the electron beam energy, and

is the normalized vector potential of the drive wave laser wave. For example, 1-TeV photons could be produced with an 8.5 lo2' W/cm2 drive pulse at 800 nm, interacting with a 550 MeV beam. By comparison, an FEL using the same laser wavelength for an electromagnetic wiggler would require over 200 GeV of beam energy.

Work supported by DoD/AFOSR (MURI) F49620-95- 1-0253, AFOSR (ATRI) F30602-94-2-001, ARO DAAH04-95-1-0336, and LLNLLDRD DOE W-7405-ENG-48 IUT B335885.

Supported by ONR and DOE. 'S.E. Harris, Phys. Rev. Lett. 77, 5357 (1996).

2C09

yRay Production in Colliding Laser Pulses

F.V. Hartemann, J.R. VanMeter and N.C. Luhmann, Jr. Dept. of Applied Science,

University of Califomia at Davis, Davis, CA A.K. Kerman

Physics Dept., Massachusetts Institute of Technology, Cambridge, MA

The acceleration of charged leptons to a TeV energies is a problem of considerable importance. At these energies, electroweak spontaneous symmetry breaking and the Higgs mechanism are expected to play a dominant role in the interaction physics. Alternatively, short wavelength photons can also be used to probe this energy range, as exemplified by the y-y collider project. We show that the combination of vacuum ponderomotive acceleration with Compton backscattering can produce high energy photons with a high intensity laser and an electron beam of relatively modest energy. In this manner, the high energy acquired by the electrons within the drive laser pulse is effectively extracted in the form of short wavelength

Wave Propagation in a Transient Anisotropic Plasma Medium-Development

of a Green's Function

Dikshitulu K. Kalluri, Tom Huang Department of Electrical Engineering, University of Massachusetts at Lowell,

Lowell, MA 01854

Transient plasmas have a time-varying plasma frequency o,(t) with a rise time T,, If the period to of a source wave existing before the transient effect begins is much larger than the rise time, the ionization change may be idealized as a sudden switching of the medium. The solution to this initial value problem with a step-change in the electron density profile is known and this profile will be considered as a reference profile. The switching action gives rise to new waves whose frequencies are either upshifted or downshifted.

The topic of this paper is the solution of the initial value problem when to is comparable to the rise time T,. The initial motivation for investigating the problem is given below.

Using the solution for the reference profile, Green's function for a switched anisotropic plasma medium is constructed. Using the Green's function a perturbation

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