• N. Thompson, M.W. Poole
  CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire
• B.W.J. McNeil
  Strathclyde University, Glasgow

Funding: We acknowledge the support of the European Framework Programme 6 EUROFEL Design Study, CCLRC, and the Scottish Universities Physics Alliance.

A Free-Electron Laser operating in the photon energy range 3-10eV is a component of the 4th Generation Light Source (4GLS) proposal at Daresbury Laboratory in the UK. In this paper we present a current design proposal which is based on the Regenerative Amplifier Free-Electron Laser (RAFEL) concept. We also present simulation results which illustrate the potential performance of the device.

• B.W.J. McNeil, G.R.M. Robb
  Strathclyde University, Glasgow
• M.W. Poole, N. Thompson
  CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire

Funding: We acknowledge the support of the European Framework Programme 6 EUROFEL Design Study, CCLRC, and the Scottish Universities Physics Alliance.

Recent proof-of-principle simulations have demonstrated a method that allows a planar undulator FEL to lase so that the interaction with an odd harmonic of the radiation field dominates that of the fundamental [1]. This harmonic lasing of the FEL is achieved by disrupting the interaction between the fundamental radiation field and electrons as they propagate through the undulator while allowing the n-th harmonic interaction to evolve unhindered. The disruption of the interaction at the fundamental is achieved by a series of relative phase changes between electrons and the fundamental ponderomotive potential of 2k pi/n (k = 1, 2, 3, . . . ; k not equal to n). The corresponding phase change with the ponderomotive potential of the n-th harmonic is then 2k pi which, at least in a simple steady-state FEL model, will have no deleterious effect upon the harmonic interaction. Such phase changes are relatively easy to implement and indeed some current FEL designs would not require any structural modification. We present a more detailed analysis of harmonic lasing and use this to discuss potential benefits and applications in extending the operational bandwidth of FELs to shorter wavelengths.

[1] B.W.J. McNeil, G.R.M. Robb and M.W. Poole, Proceedings of Particle Accelerator Conference, Knoxville, USA (2005)

• B.W.J. McNeil, G.R.M. Robb
  Strathclyde University, Glasgow
• C. Gerth
  DESY, Hamburg
• J.K. Jones, M.W. Poole, N. Thompson
  CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire

Funding: We acknowledge the support of the European Framework Programme 6 EUROFEL Design Study, CCLRC, and the Scottish Universities Physics Alliance.

An XUV Free-Electron Laser operating in the photon energy range 10-100eV is a key component of the proposed 4th Generation Light Source (4GLS) at Daresbury Laboratory in the UK. The current design proposal is an amplifier FEL seeded by a Higher Harmonic Generation (HHG) source. In this paper we present and discuss the considerations that led to the current design. We also present 3D simulation results that illustrate the potential radiation output characteristics.