CERN Accelerating science

Article
Title	Analytic Model of Harmonic Generation in the Low-Gain FEL Regime
Author(s)	Penn, Gregory
Affiliation	(LBNL/CBP, Berkeley, California LBNL, Berkeley, CaliforniaLBNL, Berkeley, California; UC Berkeley, Berkeley)
Publication	2004
In:	26th International Free Electron Laser Conference and 11th FEL User Workshop 2004, Trieste, Italy, 29 Aug - 3 Sep 2004, pp.e-proc. MOPOS57
Subject category	Accelerators and Storage Rings
Abstract	Harmonic generation using free electron lasers (FELs) requires two undulators: the first generates energy modulation through the inverse FEL effect; the second undulator uses the subsequently bunched beam to radiate at a higher harmonic. These processes are currently evaluated using extensive calculations or simulation codes which can be slow to evaluate and difficult to set up. We describe a simple algorithm to predict the output of a harmonic generation beamline in the low-gain FEL regime based on trial functions for the output radiation. Full three-dimensional effects are included. This method has been implemented as a Mathematica script which runs rapidly and can be generalized to include effects such as asymmetric beams and misalignments. This method is compared with simulation results using the FEL code GENESIS, both for single stages of harmonic generation and to model the design of LUX, a proposed facility for ultra-short X-ray pulses, where multiple stages upshift the input laser frequency by factors of up to 200.