• R. Tarkeshian, A. Azima, J. Bödewadt, H. Delsim-Hashemi, V. Miltchev, J. Roßbach, J. Rönsch-Schulenburg
  Uni HH, Hamburg
• R. Ischebeck
  PSI, Villigen
• B. Mukherjee
  Westdeutsches Protonentherapiezentrum, Essen
• E. Saldin, H. Schlarb, S. Schreiber
  DESY, Hamburg

sFLASH is a seed­ed FEL ex­per­i­ment at DESY, which uses a 38nm high har­mon­ic gain (HHG)-based XUV-beam laser in tan­dem with FLASH elec­tron bunch­es at the en­trance of a 10m vari­able-gap un­du­la­tor. The tem­po­ral over­lap be­tween the elec­tron and HHG beams is crit­i­cal to the seed­ing pro­cess. Use of a 3rd har­mon­ic ac­cel­er­at­ing mod­ule pro­vides a high cur­rent elec­tron beam (at the kA level) with ~ 600fs FWHM bunch du­ra­tion. The length of the HHG laser pulse will be ~30fs FWHM. The de­sired over­lap is achieved in steps. First is the syn­chro­niza­tion of the HHG drive laser (Ti: Sap­phire, 800nm) and the in­co­her­ent spon­ta­neous ra­di­a­tion from an up­stream un­du­la­tor. Next, the IFEL-mod­u­lat­ed elec­tron bunch will pass through a dis­per­sive sec­tion, pro­duc­ing a den­si­ty mod­u­la­tion in the beam. This in turn yields emis­sion of co­her­ent ra­di­a­tion from a down­stream un­du­la­tor or tran­si­tion ra­di­a­tion screen when the lon­gi­tu­di­nal over­lap of the two beams is achieved. The co­her­ent­ly en­hanced light emit­ted will be then spec­tral­ly an­a­lyzed. The ex­per­i­men­tal lay­out, sim­u­la­tion re­sults of gen­er­a­tion and trans­port of both light puls­es, and pre­lim­i­nary mea­sure­ments are pre­sent­ed.

• H. Delsim-Hashemi, A. Azima, J. Bödewadt, F. Curbis, M. Drescher, Th. Maltezopoulos, V. Miltchev, M. Mittenzwey, J. Roßbach, J. Rönsch-Schulenburg, R. Tarkeshian, M. Wieland
  Uni HH, Hamburg
• S. Bajt, K. Honkavaara, T. Laarmann, H. Schlarb
  DESY, Hamburg
• R. Ischebeck
  PSI, Villigen
• S. Khan
  DELTA, Dortmund
• A. Meseck
  Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Elektronen-Speicherring BESSY II, Berlin

Re­cent­ly, the free-elec­tron laser in Ham­burg (FLASH) at DESY has been up­grad­ed con­sid­er­ably. Be­sides in­creas­ing the max­i­mum en­er­gy to about 1.2 GeV and in­stal­la­tion of a third har­mon­ic rf cav­i­ty lin­eariz­ing the lon­gi­tu­di­nal phase space dis­tri­bu­tion of the elec­tron bunch, an FEL seed­ing ex­per­i­ment at wave­lengths of about 35 nm has been in­stalled. The goal is to es­tab­lish di­rect FEL seed­ing em­ploy­ing co­her­ent VUV puls­es pro­duced from a pow­er­ful drive laser by high-har­mon­ic gen­er­a­tion (HHG) in a gas cell. The pro­ject, called sFLASH, in­cludes gen­er­a­tion of the re­quired HHG puls­es, trans­port­ing it to the un­du­la­tor en­trance of a newly in­stalled FEL-am­pli­fi­er, con­trol­ling spa­tial, tem­po­ral and en­er­gy over­lap with the elec­tron bunch­es and set­ting up a pump-probe pilot ex­per­i­ment. So­phis­ti­cat­ed di­ag­nos­tics is in­stalled to char­ac­ter­ize both HHG and seed­ed FEL puls­es, both in time and fre­quen­cy do­main. Com­pared to SASE-FEL puls­es, al­most per­fect lon­gi­tu­di­nal co­her­ence and im­proved syn­chro­niza­tion pos­si­bil­i­ties for the user ex­per­i­ments are ex­pect­ed. In this paper the sta­tus of the ex­per­i­ment is pre­sent­ed.

• F. Le Pimpec, B. Beutner, H.-H. Braun, R. Ganter, C.H. Gough, C.P. Hauri, R. Ischebeck, S. Ivkovic, K.B. Li, M. Paraliev, M. Pedrozzi, T. Schietinger, B. Steffen, A. Trisorio
  PSI, Villigen

In the frame­work of the Swiss­FEL pro­ject, an al­ter­na­tive elec­tron source to an RF pho­to-gun was in­ves­ti­gat­ed. It con­sists of a high volt­age (up to 500 kV), high gra­di­ent pulsed diode sys­tem fol­lowed by sin­gle stage RF ac­cel­er­a­tion at 1.5 GHz. The elec­trons are pro­duced from pho­to-cath­odes or from field emit­ter ar­rays. The final goal of this ac­cel­er­a­tor is to pro­duce a 200 pC elec­tron beam with a pro­ject­ed nor­mal­ized emit­tance below 0.4 mm.​mrad and a bunch length of less than 10 ps. We pre­sent com­par­isons be­tween beam dy­nam­ic sim­u­la­tions and mea­sure­ments, as well as ther­mal emit­tance and quan­tum ef­fi­cien­cy (QE) mea­sure­ments ob­tained by pro­duc­ing pho­to-elec­trons from var­i­ous metal cath­odes.

• C.P. Hauri, B. Beutner, H.-H. Braun, R. Ganter, C.H. Gough, R. Ischebeck, F. Le Pimpec, M. Paraliev, M. Pedrozzi, C. Ruchert, T. Schietinger, B. Steffen, A. Trisorio, C. Vicario
  PSI, Villigen PSI

In the frame­work of the Swiss­FEL ac­tiv­i­ties at PSI we de­vel­oped a pow­er­ful UV laser sys­tem de­liv­er­ing wave­length-tun­able puls­es at a cen­tral wave­length vary­ing from 260 to 283 nm. The laser sys­tem based on a ul­tra-sta­ble fre­quen­cy-trip­pled Ti:sap­phire am­pli­fi­er de­liv­ers mJ pulse en­er­gy with­in a du­ra­tion of 1-10 ps with 1.5 nm spec­tral width. Tem­po­ral flat­top puls­es are achieved by di­rect UV shap­ing with a UV Daz­zler and a prism-based stretch­er. The sys­tem is used to ex­plore ther­mal emit­tance and quan­tum ef­fi­cien­cy de­pen­dence on pho­ton en­er­gy from metal­lic pho­to-cath­ode (Cu and Mo). With pep­per­pot tech­niques we have mea­sured the pre­dict­ed the­o­ret­i­cal limit for ther­mal emit­tance (0.4 mm.​mrad / mm rms laser spot size at 283 nm and 0.6 mm.​mrad / mm at 263 nm) for metal­lic pho­to­cath­odes.