Author: Szarmes, E.B.
Paper Title Page
MOPSO43 High Power Laser Transport System for Laser Cooling to Counteract Back-Bombardment Heating in Microwave Thermionic Electron Guns 75
 
  • J.M.D. Kowalczyk, M.R. Hadmack, J. Madey, E.B. Szarmes, M.H.E.H. Vinci
    University of Hawaii, Honolulu, HI, USA
 
  Funding: This work was funded by the Department of Homeland Security through grant #2011-DN-077-ARI055-03.
Heat from a high power, short pulse laser deposited on the surface of a thermionic electron gun cathode will diffuse into the bulk producing a surface cooling effect that counteracts the electron back-bombardment (BB) heating intrinsic to the gun. The resulting constant temperature stabilizes the current allowing extension of the gun’s peak current and duty cycle. To enable this laser cooling, high power laser pulses must be transported to the high radiation zone of the electron gun, and their transverse profile must be converted from Gaussian to top-hat to uniformly cool the cathode. A fiber optic transport system is simple, inexpensive, and will convert a Gaussian to a top-hat profile. Coupling into the fiber efficiently and without damage is difficult as tight focusing is required at the input and, if coupled in air, the high fluence will breakdown the air resulting in lost energy. We have devised a vacuum fiber coupler (VFC) that allows the focus to occur in vacuum, avoiding the breakdown of air, and have successfully transported 10 ns long, 85 mJ pulses from a 1064 nm Nd:YAG laser through 20 m of 1 mm diameter fiber enabling testing of the laser cooling concept.
 
 
TUPSO45 Initial Streak Camera Measurements of the S-band Linac Beam for the University of Hawaii FEL Oscillator 325
 
  • A.H. Lumpkin
    Fermilab, Batavia, USA
  • M.R. Hadmack, J.M.D. Kowalczyk, J. Madey, E.B. Szarmes
    University of Hawaii, Honolulu, HI, USA
 
  Funding: Work at Fermilab supported by Fermi Research Alliance, LLC under U.S.DOE Contract No.DE-AC02-07CH11359. Work at UH supported by U.S. Dept. of Homeland Security grant No. 20120-DN-077-AR1045-02.
The S-band linac driven Mark V free-electron laser oscillator (FELO) at the University of Hawai‘i operates in the mid-IR at electron beam energies of 40-45 MeV with a four microsecond macropulse length. Recently investigations of the electron beam micropulse bunch length and phase as a function of macropulse time became of interest for potentially optimizing the FELO performance. These studies involved the implementation of a Hamamatsu C5680 streak camera with dual sweep capabilities and the transport of optical transition radiation (OTR) generated at an upstream Cu mirror and of coherent spontaneous emission radiation (CSER) generated in the undulator to the streak camera location outside of the linac tunnel. Both a fast single-sweep vertical unit and a synchroscan unit tuned to 119.0 MHz were used. Initial results include measurements of the individual CSER (on the FEL7th harmonic at 652 nm) micropulse bunch lengths (3 to 5 ps FWHM), the CSER signal intensity variation along macropulse time, and a detected phase slew of 4 ps over the last 700 ns of the macropulse. Complementary OTR measurements are also being evaluated and will be presented as available.