Author: Hao, H.
Paper Title Page
High Precision Polarization Diagnostic System for Free-Electron Laser  
  • J. Yan, H. Hao, S.F. Mikhailov, V. Popov, G. Swift, Y.K. Wu
    FEL/Duke University, Durham, North Carolina, USA
  In the Duke storage ring FEL facility, an upgrade of the undulator system has created research opportunities to explore novel modes of storage ring FEL operation using as many as four helical undulators simultaneously. Recently, the generation of a linearly polarized FEL beam with the rotatable polarization direction has been realized using two sets of helical undulators of opposite helicities. To study and optimize this new FEL, high-precision polarization diagnostics are being developed to cover a wide range of wavelength from infrared (IR) to visible (VIS) to vacuum ultraviolet (VUV). In this work, we report the development of the first IR-VIS-UV polarization diagnostic system for Duke FEL operations from 1 micron to about 350 nm. This system is capable of measuring the FEL beam Stokes parameters using the extracted FEL beam. High precision measurements of FEL beam polarization have been demonstrated using a set of carefully calibrated optics.  
TUC01 Polarization Control of Storage Ring FELs Using Cross Polarized Helical Undulators 1
  • J. Yan, H. Hao, S.F. Mikhailov, V. Popov, Y.K. Wu
    FEL/Duke University, Durham, North Carolina, USA
  • S. Huang
    PKU, Beijing, People's Republic of China
  • J.L. Li
    IHEP, Beijing, People's Republic of China
  • V. Litvinenko
    Stony Brook University, Stony Brook, USA
  • N.A. Vinokurov
    BINP SB RAS, Novosibirsk, Russia
  For more than two decades, accelerator researchers have been working to gain control of polarization of synchrotron radiation and FELs using non-optical means. In 2005, the first experimental demonstration of polarization control of an FEL beam was realized with the Duke storage-ring FEL. With the recent upgrade of the undulator system, the Duke FEL can be operated with up to four helical undulators simultaneously. Using two sets of helical undulators with opposite helicities, for the first time, we have demonstrated full polarization control of a storage ring FEL. First, the helicity switch of the FEL beam has been realized with good lasing up to a few Hz. Second, the linearly polarized FEL beam has been generated with a high degree of polarization (Plin>0.95). The FEL polarization direction can be fully controlled using a buncher magnet. Furthermore, the use of non-optical means to control the FEL polarization allows us to extend polarization control to gamma-ray beams generated using Compton scattering. This has been experimentally demonstrated with the production of linearly polarized Compton gamma-ray beams with rotatable polarization direction based upon helical undulators.  
slides icon Slides TUC01 [5.916 MB]