• W. Leemans, E. Esarey, G. Fubiani, C.G.R. Geddes, P. Michel, B. Nagler, K. Nakamura, C.B. Schroeder, B. Shadwick, C. Toth, J. Van Tilborg
  LBNL, Berkeley, California
• D.L. Bruhwiler
  Tech-X, Boulder, Colorado
• J.R. Cary
  CIPS, Boulder, Colorado
• C. Filip, E. Michel
  University of Nevada, Reno, Reno, Nevada
• A.J. Gonsalves, S.M. Hooker
  OXFORDphysics, Oxford, Oxon

Laser driven accelerators are capable of producing energetic electron beams using ultra-high gradients on the order of 10^-100 GV/m. Prior to 2004, experiments had demonstrated high energy acceleration but with 100 % energy spread. Recent experiments have shown that 100 MeV class intense electron beams with narrow energy spread [1-3] can be generated in mm-scale structures. At the multi-beam L’OASIS facility at LBNL we have produced beams with narrow energy spread using a channel guided laser accelerator [1]. As opposed to single beam experiments, two additional laser beams are used to first produce a plasma channel which then guides an intense drive laser beam over greater distances than in single beam experiments. By properly controlling the channel, 100 MeV-class beams were produced with few percent energy spread, containing 0.3 nC of charge and with a normalized emittance around 1-2 π mm-mrad. Characterization of the bunch length and shape is underway using an electro-optic technique operating in the THz regime that has been implemented and tested using single-beam experiments. Experiments have started to increase the energy to the GeV-level. Hydrogen filled capillary discharges are used to guide beams from the 100 TW-class LOASIS laser and, to date, guiding of 5x1017 W/cm2 over 33 mm has already been shown. Such structures are expected to produce GeV electron beams when laser intensities exceeding 2x1018 W/cm2 are realized. If the normalized emittance from the 100 MeV beams remains preserved and the relative energy spread is reduced during acceleration, such a beam could be used for development of a laser wakefield driven FEL.

[1] C.G.R. Geddes et al., Nature 431, 538- 541(2004). [2] S.P.D. Mangles et al., Nature 431, 535 –538 (2004). [3] J. Faure et al., Nature 431, 541-544 (2004).

• M. Goldstein, S.H. Lee, Y.A. Shroff, P.J. Silverman, D. Williams
  Intel, Santa Clara, California
• R. Pantell
  Stanford University, Stanford, Califormia
• H. Park, M.A. Piestrup
  Adelphi Technology, Inc., San Carlos, California

Funding: Intel Research

Semiconductor industry growth has largely been made possible by regular improvements in lithography. State of the art lithographic tools cost upwards of twenty five million dollars and use 0.93 numerical aperture projection optics with 193nm wavelengths to pattern features for 45 nm node development. Scaling beyond the 32 nm feature size node is expected to require extreme ultraviolet (EUV) wavelength light. EUV source requirements and equipment industry plasma source development efforts are reviewed. Exploratory research on a novel hybrid klystron and high gain harmonic generation FEL with oblique laser seeding will be disclosed. The opportunity and challenges for FELs to serve as a second generation (year 2011-2013) source technology in the semiconductor industry are presented.

• S. Reiche, C. Joshi, C. Pellegrini, J.B. Rosenzweig, S. Tochitsky
  UCLA, Los Angeles, California
• G. Shvets
  The University of Texas at Austin, Austin, Texas

Funding: The work was supported by the DOE Contract No. DE-FG03-92ER40727.

Free-Electron Laser in the THz range can be used to generate high output power radiation or to modulate the electron beam longitudinally on the radiation wavelength scale. Microbunching on the scale of 1-5 THz is of particular importance for potential phase-locking of a modulated electron beam to a laser-driven plasma accelerating structure. However the lack of a seeding source for the FEL at this spectral range limits operation to a SASE FEL only, which denies a subpicosecond synchronization of the current modulation or radiation with an external laser source. One possibility to overcome this problem is to seed the FEL with two external laser beams, which difference (beatwave) frequency is matched to the resonant FEL frequency in the THz range. In this presentation we study feasibility of an experiment on laser beat-wave injection in the THz FEL considered at the UCLA Neptune Laboratory, where both a high brightness photoinjector and a two-wavelength, TW-class CO₂ laser system exist. By incorporating the energy modulation of the electron beam by the ponderomotive force of the beat-wave in a modified version of the time-dependent FEL code Genesis 1.3, the performance of a FEL at Neptune is simulated and analyzed.

• B.W. Adams
  ANL, Argonne, Illinois

Funding: U.S. Department of Energy, Office of Basic Energy Sciences under contract W-31-109-ENG-38

A way is proposed to obtain intense infrared/visible light from an electron bunch in an x-ray free-electron laser in femtosecond synchronism with the x-rays themselves. It combines the recently proposed technique of emittance slicing in a free-electron laser with transition undulator radiation (TUR). The part of the electron bunch that is left unspoiled in the emittance slicing process is the source of both coherent x-rays and of coherent TUR at near-infrared wavelengths. An extension of the concept also exploits the fact that the electrons that participate in the free-electron lasing process lose a significant part of their energy.

• 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)

• C. Pellegrini, J.B. Rosenzweig, G. Travish
  UCLA, Los Angeles, California
• V.A. Dolgashev, C.D. Nantista, S.G. Tantawi
  SLAC, Menlo Park, California

Funding: US Department of Energy

We describe a proposed high-gain FEL using an X-band microwave undulator and operating at a wavelength of about 0.5 μm. The FEL electron beam energy is 65 MeV. The beam is produced by the NLCTA X-band linac at SLAC, using an S-band high-brightness photoinjector. The undulator consists of a circular waveguide with an rf wave counter-propagating with respect to the electron beam. The undulator is powered with two high-power X-band klystrons and a dual-moded pulse compressor recently developed at SLAC. This system is capable of delivering flat-top rf pulses of up to 400 ns and a few hundred megawatts. The equivalent undulator period is 1.4 cm, the radius of the circular pipe is 1 cm, and the undulator parameter is about 0.4 for a helical undulator configuration, obtained using two cross-polarized TE modes, or larger for a planar configuration, using one rf polarization. The undulator is about four meters long. The FEL will reach saturation within this distance when operated in a SASE mode. We describe the FEL performance parameters, the undulator characteristics and tolerances. One main goal of the experiment is to demonstrate the feasibility of an rf undulator for high gain FELs.