• E. Hemsing, A. Marinelli, P. Musumeci, J.B. Rosenzweig, R. Tikhoplav
  UCLA, Los Angeles, California
• A. Gover
  University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
• S. Reiche
  PSI, Villigen

The resonant harmonic interaction of an electron beam (e-beam) with an EM input field in a helical undulator is explored. The e-beam is coupled to the input radiation field at frequency harmonics through transverse gradients in the EM field, and helical micro-bunching of the e-beam is shown to occur naturally at the higher harmonics with the injection of a simple gaussian laser mode onto a cylindrically symmetric e-beam. This approach is under investigation as a method to generate a strongly pre-bunched e-beam seed for superradiant emission of light that carries orbital angular momentum in a downstream free-electron laser.

• A. Knyazik, J.B. Rosenzweig, R. Tikhoplav
  UCLA, Los Angeles, California

A helical undulator, utilizing permanent-magnet of cylindrically symmetric (Halbach) geometry has been developed at UCLA’s Neptune Facility. The initial prototype is a short 10 cm, 7 periods long helical undulator, designed to test the electron-photon coupling by observing the micro-bunching has been constructed and is currently being tested in the Neptune facility. An Open Iris-Loaded Waveguide Structure (OILS) scheme which conserves laser mode size and wave fronts throughout the undulator, is utilized to avoid Gouy phase shift caused by focusing of the drive laser. Coherent Transition Radiation and Coherent Cherenkov Radiation is used for micro-bunching diagnostic. Currently the undulator has been built, magnets were calibrated via pulsed wire method.

• A.M. Cook, J.B. Rosenzweig, R. Tikhoplav, S. Tochitsky, G. Travish, O. Williams
  UCLA, Los Angeles, California

Funding: Work supported by DOE.

We report experimental observation of narrow-bandwidth pulses of coherent Cherenkov radiation produced when a sub-picosecond electron bunch travels along the axis of a hollow circular cylindrical dielectric-loaded waveguide. For an appropriate choice of dielectric structure properties and driving electron beam parameters, the device operates in a single-mode regime, producing radiation in the THz range. We present measurements showing the emission of a narrowly-peaked spectrum from a fused silica tube 1 centimeter long with sub-millimeter transverse dimensions. We discuss the agreement of this data with theoretical and computational predictions, as well as possibilities for future study and application.

• R. Tikhoplav, G. Travish
  UCLA, Los Angeles, California
• G. Andonian, A.Y. Murokh, M. Ruelas
  RadiaBeam, Marina del Rey
• T.V. Shaftan, V. Solovyov
  BNL, Upton, Long Island, New York

Funding: NSF grant # IIP-0724505

We describe our effort in the development of a low cost, wide-band detector/camera for generation of spatially resolved images of radiation beams in a multi-spectral range of wavelengths, from IR (infrared) to THz (terahertz). The detector (T-camera) utilizes a TLC (thermochromic liquid crystal) film as the sensitive element in a temperature controlled chamber and a CCD detector array and can be used as a powerful diagnostic for terahertz sources such as a synchrotron or an FEL