Free Electron Laser Studies. David Dunning MaRS ASTeC STFC Daresbury Laboratory. Free Electron Laser (FEL) Studies. What is a free electron laser? And why are we interested? How does a free electron laser work? What is the current state of the art? What are we working on?
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STFC Daresbury Laboratory
Extremely useful output properties:
Accelerator-based photon source that operates through the transference of energy from a relativistic electron beam to a radiation field.
E fieldHow does an FEL work?
vzWhat is a FEL?
A classical source of tuneable, coherent electromagnetic radiation due to accelerated charge (electrons)
NOT a quantum source!
2nd HarmonicResonant wavelength, slippage and harmonics
Harmonics of the fundamental are also phase-matched.
Resonant emission – electron bunching
Electrons bunch at resonant radiation wavelength – coherent process
Axial electron velocity
Low-gain FELs use a short undulator and a high-reflectivity optical cavity to increase the radiation intensity over many undulator passes
High-gain FELs use a much longer undulator section to reach high intensity in a single pass
Self-amplified spontaneous emission (SASE)
*B W J McNeil, J A Clarke, D J Dunning, G J Hirst,
H L Owen, N R Thompson, B Sheehyand P H Williams,
Proceedings FEL 2006
New Journal of Physics 9, 82 (2007)
SASESpike FWHM ~ 10fs
Mode-CoupledSpike FWHM ~ 1 fs
Mode-LockedSpike FWHM ~ 400 as
Neil Thompson and Brian McNeil, PRL, 2007
Mode locking mechanism
Brian McNeil, David Dunning, Neil Thompson and Brian Sheehy, Proceedings of FEL08
Drive λ=805.22nm, h =65, σt=10fsAmplified HHG – retaining structure
HHG amplification mechanism
HHG amplification mechanism with energy modulation period and slippage at multiple of pulse spacing
Five 2.2m undulator modules. Gain 10,000%
2mm outcoupling hole: outcoupling fraction ~75%VUV-FEL: Main features