1. Free Electron Lasers (FEL’s)
Toon Coenen

2. Outline Introduction FEL’s Laser characteristics
Power output calculation
Research
Conclusion
Photon Physics Laser presentation

3. Introduction Bound electrons Population inversion Coherent radiation
Free electrons in vacuum
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4. FEL’s Photocathode Accelerator Relativistic speeds Undulator
Periodic magnetic field
Oscillations
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5. FEL’s
Point dipoles
Low energy (electron frame)→ High energy (lab frame)
Blue shift
Kinetic energy electron
Tune emission wavelength
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6. FEL’s Conventional design Laser Cavity Standing wave
Impossible for λ<150nm
Mirrors
Mirror
Undulator
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7. FEL’s Single pass FEL’s SASE Micro-bunching Hard x-ray laser
XFEL in Hamburg
~3.4 km long
Operational in 2015
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8. Laser Characteristics
Silfvast
European XFEL
Laser wavelengths
248 nm to 8 mm
0.06 to 0.4 nm
Laser gain medium length
1–25 m m
Pumping method
Electron beam
Electron beam pulse length
2 ps to cw
200 fs
Electron beam energy
200 keV to 1 GeV
17.5 GeV
Electron beam peak current A
5 kA
Undulator magnet period
5 mm to 0.2 m
26 mm
Magnetic field strength
0.02 to 1T
0.28 to1.24T
Output power
Up to GW(pulsed), 10W (cw)
20 to 150 GW (pulsed)
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9. Power Output Stanford FEL
Power within the cavity:
PC = N2*P/(1-(1-T)1/2)2
N = 2.94*107 electrons
P = 3.24 *10-14W
T = 1.5 %
Output power:
Pout = PCT = 7.4 kW
Properties
Values
Wavelenght
2.8 μm
Electron pulse length
0.13 cm
Pulse spacing
84.6 ns
Electron energy
43.5 MeV
Beam radius
0.03 cm
Magnetic Field period
3.22 cm
Field strength
0.24 T
Interaction length
5.2 m
Cavity length
12.7 m
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10. Single shot ultrafast diffraction
λ =32nm
tp=25 fs
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11. Conclusion Tune device to match needs Wavelenghts up to x-rays
High output power
Short pulses
Sources:
[1] W. T. Silfvast, Laser Fundamentals 2nd edition 2004, chapter 14.4
[2] Technical design report European XFEL
[3] Y.W. Chan, W.L. Tsui, On the output power of a magnetic free electron laser, Physics letters, October 1979
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12. Questions?
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