Author: Lindau, F.
Paper Title Page
THOB4 Transverse Coherence and Polarization Measurement of Coherent Femtosecond Pulses from a Seeded FEL 458
 
  • J. Schwenke, N. Čutić, F. Lindau, S. Werin
    MAX-lab, Lund, Sweden
  • E. Mansten
    Lund University, Division of Atomic Physics, Lund, Sweden
  
  We re­port on mea­sure­ments of the trans­verse co­her­ence and po­lar­iza­tion of light pulses at 131 nm gen­er­ated by a seeded free-elec­tron laser. Our setup con­sists of two un­du­la­tors. The first un­du­la­tor is used to en­ergy mod­u­late rel­a­tivis­tic elec­tron bunches (375 MeV) with the help of an ul­tra­vi­o­let seed laser pulse at 263 nm. The elec­tron bunches sub­se­quently pass through a dis­per­sive sec­tion, where the en­ergy mod­u­la­tion is con­verted into mi­crobunch­ing, and then enter the ra­di­a­tor un­du­la­tor. The ra­di­a­tor is an AP­PLE-II type un­du­la­tor set to be in res­o­nance for 131 nm ra­di­a­tion. The ra­di­a­tor emits co­her­ent fem­tosec­ond pulses up to the 6th har­monic of the seed laser [1]. The state of po­lar­iza­tion of the pulses can be tuned from pla­nar to he­li­cal po­lar­iza­tion by shift­ing the un­du­la­tor mag­nets. The emit­ted pulses are an­a­lyzed with a grat­ing spec­trom­e­ter. A dou­ble slit aper­ture is po­si­tioned in the beam in order to de­ter­mine the trans­verse co­her­ence of the light pulses by an­a­lyz­ing the fringe vis­i­bil­ity. Fur­ther­more, the gen­er­a­tion of cir­cu­lar po­lar­ized light is demon­strated. The po­lar­iza­tion state of the light pulses is mea­sured with a Ro­chon prism po­lar­izer.
[1] Cutic et al, Phys. Rev. Spec. Top-AC 14, 030706 (2011) 		 
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