Author: Friedman, A.
Paper Title Page
WEB04 Saturation Dynamics, Fine Spectrum, and Chirp Control in a CW FEL Oscillator 580
  • H. S. Marks, A. Gover, H. Kleinman
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
  • D. Borodin, A. Damti, A. Friedman, Y. Vashdi
    Ariel University, Ariel, Israel
  • M. Einat, M. Kanter, Y. Lasser, Yu. Lurie, A. Yahalom
    Ariel University Center of Samaria, Faculty of Engineering, Ariel, Israel
  As in conventional laser physics, the saturation dynamics of a long-pulse Electrostatic Accelerator FEL (EA-FEL) oscillator consists of oscillations build-up, resonator modes competition, and establishment of narrow linewidth single mode lasing. In EA-FEL the gain curve drifts to lower frequencies during the long laser pulse due to inevitable droop in the acceleration voltage. This post-saturation drift renders fine chirp of the single mode laser frequency due to the oscillator frequency pulling effect. We have integrated a voltage-ramping element into the electrostatic accelerator terminal that makes it possible to control the acceleration voltage throughout the lasing pulse. This allows us to keep the voltage constant throughout the e-beam pulse, and so increase the single mode lasing time, avoiding mode-hopping during the pulse due to the drift of the gain curve. Furthermore, by adjusting the voltage ramp rate and polarity we obtained controllable positive/negative laser frequency chirp that can be used in a single pulse sweep for fine spectral line (10-6) gas-spectroscopy. The study was conducted on the Israeli EA-FEL that operates at tunable frequencies between 95-110 GHz.  
slides icon Slides WEB04 [2.310 MB]  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
WEP085 Conceptual Theory of Spontaneous and Taper-Enhanced Superradiance and Stimulated Superradiance 746
  • A. Gover, R. Ianconescu
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
  • C. Emma, P. Musumeci
    UCLA, Los Angeles, USA
  • A. Friedman
    Ariel University, Ariel, Israel
  Funding: We acknowledge partial support by the U.S. Israel Binational Science Foundation (BSF)Jerusalem, Israel
In the context of radiation emission from an electron beam Dicke's superradiance (SR) is the enhanced radiation emission from a pre-bunched beam. Stimulated Superradiance (ST-SR) is the further enhanced emission of the bunched beam in the presence of a phase-matched radiation wave. These processes were analyzed for Undulator radiation in the framework of radiation field mode-excitation theory[1]. In the nonlinear saturation regime the synchronism of the bunched beam and an injected radiation wave may be sustained by wiggler tapering [2]. Same processes are instrumental also in enhancing the radiative emission in the tapered wiggler section of seeded FEL[3]. In a long tapered wiggler the diffraction of the emitted radiation wave is not negligible even at Angstroms wavelengths (as in LCLS). A Fresnel diffraction model was provided in [4] for the SR process only. Here we outline the fundamental physical concepts of Spontaneous Superradiadce (SR), Stimulated Superradiance (ST-SR), Taper-Enhanced Superradiance (TES) and Taper-Enhanced Stimulated Superradiance Amplification (TESSA), and compare their Fourier and Phasor formulations in the radiation mode expansion and free-diffraction models. Detailed further analysis can provide better design concepts of high power FELs and improved tapering strategy for enhancing the power of seeded short wavelength FELs
1. A. Gover, PR ST-AB 8, (030701) ; (030702) (2005)
2. J. Duris et al., arxiv 2015.
3. Y. Jiao et al., PR ST-AB 15 050704 2012
4. E.A. Schneidmiller, M.V. Yurkov, PR ST-AB 18, 030705 (2015)
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)