Keyword: lattice
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MOPSO61 Modulated Medium for Generation of Transition Radiation electron, radiation, dipole, polarization 105
 
  • K.B. Oganesyan
    ANSL, Yerevan, Armenia
 
  Funding: ISTC
It is shown on an example of amorphous quartz, under the influence of a standing microwave field, at its certain parameters, superlattice is created in the medium where difference in values of dielectric constants of neighboring layers can be up to third order. This superlattice exists during the nanosecond, however it is sufficient for using it as a radiator for generation of transition radiation by relativistic electrons.
 
 
TUPSO49 Electric Field Dependence of Photoemission From n- and p- Type SI Crystals FEL, cathode, free-electron-laser, laser 339
 
  • S. Mingels, B. Bornmann, D. Lützenkirchen-Hecht, G. Müller
    Bergische Universität Wuppertal, Wuppertal, Germany
  • C. Langer, C. Prommesberger, R. Schreiner
    Regensburg University of Applied Sciences, Regensburg, Germany
 
  Funding: Funding Agency: German Federal Ministry of Education and Research BMBF (contract number 05K10PXA)
The performance of free electron lasers depends on the brilliance of the electron source*. Nowadays photocathodes (e.g. Cs­2Te) are used despite of their high emittance. To develop robust and more brilliant cathodes we have built up an UHV system which enables systematic photoemission (PE) measurements with a tunable pulsed laser (W=0.5-5.9 eV) at high electric fields (E<400 MV/m)**. First results on Au and Ag crystals revealed only low quantum efficiency (QE) due to fast electron relaxation. Hence, we have started QE(W,E) investigations on n- and p-Si wafers. Resonant PE was observed above as well as below the work function F, which can be allocated to optical transitions in the band structure of Si or explained by thermally excited states at the bottom of the conduction band. As expected, only low QE values were achieved even for n-Si probably due to surface oxide. Moreover, a significant rise of the QE peaks above F were obtained for n-Si already at E=8-9 MV/m, which was limited by discharges due to surface pollution. Detailed results and a discussion on the potential of semiconductors as highly brilliant photo-induced field emission cathodes will be presented at the conference.
*D.H. Dowell et al., Nucl. Instr. And Meth. Phys. A 622, 685-697 (2010)
**B. Bornmann et al., Rev. Sci. Instrum. 83, 013302 (2012)