WEOBNO —  Long Wavelength   (28-Aug-13   11:30—12:30)
Chair: H. Ohgaki, Kyoto University, Institute for Advanced Energy, Kyoto, Japan
Paper Title Page
WEOBNO01
 Design and Simulation of CAEP THz FEL  
 
  • Y.H. Dou, X.J. Shu
    Institute of Applied Physics and Computational Mathematics, People's Republic of China
  • X. Yang
    CAEP/IAE, Mianyang, Sichuan, People's Republic of China
  
  Funding: The work was supported by National Natural Science Foundation of China under Grant 11105019; National Major Instrumentation Special under Grant 2011YQ130018 and Project 2011B0401066 supported by CAEP.
Design and simulation of CAEP THz free electron laser (FEL) have been carried out using our 3D-OSIFEL code. The main work focuses on the optimization to different parameters of optical resonator and wiggler. The wiggler peak field strength and electron beam energy have been selected with eleven frequencies ranging from 1 THz to 3 THz. The gain and power of resonator are calculated, which are corresponding to eleven frequencies. It can be seen by simulation results that when facility works at 2.6 THz, the gain and output power are the highest in the frequency range from 1 THz to 3 THz. So the experiment may be conducted at this frequency first. When the device works toward 1 THz, the slippage length and the loss of optical resonator will increase due to the increase of the radiation wavelength, which results in the reduction of the gain and output power. So experiment running at 1THz could be challenged and the scheme of elliptical hole-coupling optical resonator is proposed to solve the problem. The simulation results show that the elliptical hole-coupling output is effective and applicable for the THz FEL and the output power can be increased by more than 30%. 		 
 
WEOBNO02
 Improving the Pulse Characteristics of Mid-IR FEL for Ultrafast Spectroscopy  
 
  • T. Nakajima, T. Kii, H. Ohgaki, Y. Qin, X. Wang, H. Zen
    Kyoto University, Institute for Advanced Energy, Kyoto, Japan
  
  The FEL we have developed at Kyoto University, KU-FEL, is an oscillator-type FEL in the mid-infrared. The micropulse duration is 0.6 ps, the time interval between the successive micropulses is 350 ps, and the wavelength stability is 1.3% [1]. This pulse structure is not a problem at all for many applications in which the fluence of FEL itself plays a major role. However, for some applications, such a pulse structure spoils the time resolution. To improve the pulse characteristics of KU-FEL for ultrafast spectroscopy we have developed a simple two-stage optical system after the FEL output. In the first stage we introduce double plasma shutters for the ultrafast switching-on/off of a pulse train. In the second stage we introduce a bulk nonlinear material with several mm thickness to broaden the FEL spectrum through self-phase modulation so that we do not have to scan the FEL wavelength during the measurement. A combined use of this two-stage optical system and the single-shot spectral measurement technique we have recently developed for the mid-infrared wavelength region [2], we are now ready to perform single-shot ultrafast spectroscopy without scanning the FEL wavelength.
[1]Qin, Zen, Wang, Kii, Nakajima, and Ohgaki, Optics Letters 38, 1068 (2013).
[2]Wang, Nakajima, Zen, Kii, and Ohgaki, Optics Letters 37, 5148 (2012).
 		 
 
WEOBNO03 Intense Emission of Smith-Purcell Radiation at the Fundamental Frequency from a Grating Equipped with Sidewalls 477
 
  • J.T. Donohue
    CENBG, Gradignan, France
  • J. Gardelle, P. Modin
    CEA, LE BARP cedex, France
  
  The two-dimensional theory of the Smith-Purcell free-electron laser predicts that coherent Smith-Purcell radiation can occur only at harmonics of the frequency of the evanescent wave that is resonant with the beam. Particle-in-cell simulations have shown that in a three-dimensional context, where the lamellar grating has sidewalls, coherent Smith-Purcell radiation can be copiously emitted at the fundamental frequency, for a well-defined range of beam energy. An experiment at microwave frequencies has confirmed this prediction . The power output is considerably greater than for the previously observed emission at the second harmonic, in agreement with three-dimensional simulations . The dependence of frequency on beam energy and emission angle is in good agreement with three-dimensional theory and simulations. Provided that a reduction in scale can be achieved, a path is open to coherent Smith-Purcell radiation at Terahertz frequencies.
(1) J. Gardelle, P. Modin and J.T. Donohue, Appl. Phys. Lett. 100, 131103 (2012).
(2) J. T. Donohue and J. Gardelle, Appl. Phys. Lett. 99, 161112 (2011).
 		 
slides icon Slides WEOBNO03 [11.891 MB]  
 
WEOBNO04
 Integration of Accelerator Based IR/THz Source for Pump Probe Experiments in the Infrastructure of the European XFEL  
 
  • M.V. Yurkov, E. Schneidmiller
    DESY, Hamburg, Germany
  • M. Gensch
    HZDR, Dresden, Germany
  • M. Izquierdo
    XFEL. EU, Hamburg, Germany
  • M. Krasilnikov, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
  
  We analyze the scope of pump-probe experiments at the European XFEL involving IR/THz and x-ray pulses. Different experiments impose different requirements on the properties of the IR/THz source like wavelength range, spectral properties, intensity, pulse duration, polarization, synchronization capabilities, repetition rate, etc. Our previous analysis have shown that the most universal solution of the problem of the IR/THz radiation source is an accelerator based source. The electron accelerator is similar to that operating at the PITZ facility. It consists of an rf gun and a warm (or cold) accelerating section. Powerful, coherent radiation with prescribed temporal, spectral and polarization properties is generated in a set of radiators like undulators (using mechanism of SASE FEL for short wavelength and coherent undulator radiation for long wavelength), edge radiators, OTR foils, diffraction radiators. Location of the electron source close to the experiment would allow performing of pump-probe experiments involving also ultrashort electron pulses. In this paper we discuss problems of the integration of the accelerator based THz source into infrastructure of the European XFEL.  
slides icon Slides WEOBNO04 [3.339 MB]