• E.J. Montgomery, D.W. Feldman, P.G. O'Shea
  UMD, College Park, Maryland
• J.R. Harris, J.C. Jimenez
  NPS, Monterey, California
• K. L. Jensen
  NRL, Washington, DC

Photocathodes are a promising electron source for future high average current FELs, with ps response, kA/cm² peak and A/cm² average current, but will require delicate cesium-based coatings to achieve requisite quantum efficiency (QE). The UMD dispenser photocathode replenishes cesium from a subsurface reservoir, extending lifetime [1]. Recesiation has been shown to reverse oxidizer-induced QE loss [2]. Optimization of pore size and spacing will enable uniform recesiation without emitting excess cesium into the cavity. We here quantify for the first time cesium emission from active dispenser photocathodes and summarize status of experimental and modeling efforts.

[1] N.A. Moody et.al., Appl. Phys. Lett. 90, 114108 (2007).
[2] E.J. Montgomery et al., AIP Conf. Proc. {10}86, 599 (2009).

• C. Callegari, K.C. Prince
  ELETTRA, Basovizza
• T. Möller
  Technische Universität Berlin, Berlin
• F. Stienkemeier
  Physikalisches Institut Albert-Ludwig, Freiburg
• S. Stranges
  Università di Roma "La Sapienza", Roma

The Low Density Matter beamline (LDM) at FERMI@Elettra is scheduled to begin operation in early 2011 as a large collaborative project for experiments on neutral matter beams, and later on trapped species and mass selected ions. FERMI@Elettra is a seeded source comprising two Free Electron Lasers(FELs) that will generate short pulses (25–200fs) of VUV (FEL1:12-60eV) and XUV/soft-X-rays (FEL2:60-300eV; third harmonic: up to 900eV) with close-to-transform-limited transverse and longitudinal coherence, and full polarization control. It includes a synchronized broadly-tunable user laser for pump-probe experiments. LDM modular design seeks to exploit these unique features with a flexible choice of target system and detection method. It will supply intense beams of neutral atoms, closed-shell molecules, radicals, and pure/doped clusters (the latter ranging from ultracold helium nanodroplets, to atomic and molecular van der Waals clusters, especially water, to clusters of refractory materials such as metals and their oxides). These can be combined with a set of detectors, working in tandem when possible, for photoelectron/photoion spectroscopy, fluorescence emission, and photon scattering.