• A.I. Al-Shamma'a, J. Lucas, A. Shaw, R.A. Stuart, C.C. Wright, M. Houghton
  University of Liverpool, Liverpool
• P. van der Slot
  University of Twente
• J. Hamelin
  University of Rennes

The objectives of this European project are to use high frequency microwave technology to develop focused energy sources for industrial applications. The microwaves, generated in the 10GHz to 20GHz frequency range by using a table top FEM has been used to investigate novel solutions for material processing and material production, including microwave heating of substrates, microwave chemistry for increasing the speed of thermal reactions, microwave plasma chemistry for aiding gaseous reactions in the reduction of combustion pollutants and the production of UV/ozone for germicidal activities. In this paper we report unique results and analysis in using tuneable FEM system compared with the conventional magnetron 2.45 GHz system.

• R. Tatchyn
  SLAC, Menlo Park, California

The temporal resolution of pump-flash interactions in the ultrashort (fs-as) regime is limited by the characteristic time constants of the excited states in the detector material. If the relaxation time constant is appreciably longer that the time interval between the pump and probe signals the response of the detector material to the probe represents a temporal convolution of the pump and probe responses, setting a lower limit on the resolution to which the interval between the two pulses can be measured. In most of the solid state ultrafast detection schemes that are being considered for the ultra-short pulse x-ray sources under current development at SLAC and elsewhere the characteristic time constants are related to the bound states of the atoms comprising the material or to the relaxation times of phase transitions or charge carrier populations of the lattice, setting a probable lower limit on the attainable resolution on the order of ~0.1 ps. In this paper we consider a novel detection principle predicated on the excitation of specially prepared unbound states in an ionized plasma and estimate its potential for extending the lower limit of resolution into the as regime.

• C.A. Brau, H.L. Andrews, C.H. Boulware, J.D. Jarvis
  Vanderbilt University, Nashville, Tennessee

Funding: Medical Free Electron Laser Program of the Department of Defense under grant number F49620-01-1-0429.

In a SP-FEL, the electrons interact with an evanescent mode of the grating whose frequency is below the lowest frequency for SP radiation [1] and which travels along the grating with no losses except from dissipation. At low electron energy, the group velocity is negative and the SP-FEL operates on an absolute instability; no optical resonator is required. Due to the finite conductivity of the grating surface, dissipative losses attenuate the evanescent wave [2]. Computations for a lamellar grating show that attenuation is important at frequencies above 1 THz, and dominates when the group velocity is small. Due to the interaction with the evanescent wave, the electrons are bunched at the evanescent wave frequency. The superradiant emission from periodic bunches is characterized by spectral and angular narrowing at harmonics of the bunching frequency. Experiments are in progress to demonstrate these effects using a 40-keV electron beam photoemitted from a needle cathode in 5-ns pulses. The grating is 15 mm long, with a 250-micron period. We expect lasing at a wavelength near 1 mm, which will allow us to observe superradiant emission near 330 microns (third harmonic of the evanescent wave) on the second order of the SP radiation.

[1] H. L. Andrews and C. A. Brau, Phys. Rev. ST-AB 7, 070701 (2004). [2] H. L. Andrews, et al., Phys. Rev. ST-AB (in press).