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Title page for ETD etd-01292007-223843


Type of Document Dissertation
Author Boulware, III, Charles H.
URN etd-01292007-223843
Title Electron Beams from Needle Photocathodes and a New Theory of the Smith-Purcell Free-Electron Laser
Degree PhD
Department Physics
Advisory Committee
Advisor Name Title
Charles A. Brau Committee Chair
David Piston Committee Member
Leonard C. Feldman Committee Member
Marcus Mendenhall Committee Member
Richard Haglund Committee Member
Keywords
  • needle photocathode
  • Smith-Purcell free-electron laser
Date of Defense 2007-01-19
Availability unrestricted
Abstract
A promising source of radiation in the important terahertz (THz) region of the spectrum is the Smith-Purcell free-electron laser (SPFEL). This dissertation presents a new theory of the SPFEL, taking into account dispersion of evanescent surface waves on the grating. From the dispersion relation for these waves, it is found that the device can operate as an amplifier or as an oscillator. The gain length is calculated in the amplifier regime, as well as the growth rate and start current in the oscillator regime. The theory is supported by published computer simulations, but in conflict with previous experiment.

These devices require a high-quality electron beam, and this dissertation also presents developments in needle photocathodes designed to drive an SPFEL. Data on emission current are presented as a function of voltage for various drive laser wavelengths. A simplified model is used to interpret the data as variation in the emitting area with voltage for photon energies below the cathode workfunction. Data and a new scaling law for the divergence of the beam at high current are also presented.

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