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Freund, H.

Paper Title Page
MOPPH003 The Effect of Shot-Noise on the Start-Up of the Fundamental and Harmonics in Free-Electron Lasers 9
 
  • H. Freund, W. H. Miner
    SAIC, McLean
  • L. Giannessi
    ENEA C. R. Frascati, Frascati (Roma)
  
  The problem of radiation start-up in FELs is important in the simulation of virtually all FEL configurations including oscillators and amplifiers in both seeded-MOPA (Master Oscillator Power Amplifier) and SASE (Self-Amplified Spontaneous Emission) modes. Both oscillators and SASE FELs start up from spontaneous emission due to shot-noise that arises from the random fluctuations in the electron phase distribution. The injected power in a MOPA is usually large enough to overwhelm the shot-noise; however, this noise must be treated correctly to model the initial start-up of the harmonics. We discuss and compare two different shot noise models that are implemented in both 1D wiggler-averaged (PERSEO) and non-wiggler-averaged (MEDUSA1D) simulations, and a 3D, non-wiggler-averaged (MEDUSA) formulation. These models are compared for examples describing both SASE and MOPA configurations in 1D in steady-state and time-dependent simulations, and remarkable agreement is found between PERSEO and MEDUSA1D. In addition, 3D correction factors have been included in the MEDUSA1D and PERSEO, and show reasonable agreement with MEDUSA for a sample MOPA in steady-state and time-dependent simulations.  
MOPPH007 Optical Beam Quality in Free-Electron Lasers 21
 
  • H. Freund
    SAIC, McLean
  • B. Hafizi
    Icarus Research, Inc., Bethesda, Maryland
  • J. Penano, P. Sprangle
    NRL, Washington, DC
  
  The mode quality of the output of free-electron lasers (FELs) is near the diffraction limit. In this paper, we analyze the optical mode quality in FELs using the M2 parameter, which is a measure of the size and divergence of the optical beam. We calculate M2 in two ways:
  1. by a direct integration over the transverse mode structure, and
  2. by allowing the mode to expand beyond the wiggler and analyzing the divergence.
A numerical analysis is conducted using the MEDUSA simulation code that shows that M2, as expected, is near unity at saturation but increases with the higher order mode content if the interaction proceeds past saturation. 		 
MOPPH034 Mirror Aberrations in Low Gain FEL Oscillators 63
 
  • P. J.M. van der Slot, K.-J. Boller, R. van der Meer
    Mesa+, Enschede
  • H. Freund
    SAIC, McLean
  
  To generate radiation with high spatio-temporal quality in FELs, oscillators are to be used whch are based on the combination of low gain with a large number of roundtrips in a low-loss optical resonator. Clearly, in this situation any additional loss or aberration may seriously degrade the performance and beam quality, and this becomes extremely important for high average power FEL oscillators such as the JLAB system*. Nevertheless, so far no systematic study has been made how various mirror aberrations affect the performance of such low gain FEL oscillators. Here we present the first results of such a study. Ths approach is based on the optical propagation code OPC** with the Genesis 1.3*** gain code.

* SV Benson et.al. Nucl. Instr. and Meth. A483, 434 (2002).
** JG Karssenberg, et.al. J. Appl. Phys. 100, 093106 (2006).
*** http://pbpl.physics.ucla.edu/~reiche/