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Tutorial on FELby Sverker Werin
FEL Free Electron Laser
?Light Amplification by Synchronised Electron
Retardation
As opposed to bound electrons
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Energy exchange light ? e- Bunching Radiation
Amplification
Basics
CavityFEL
CHGCoherent Harmonic Generation
Concepts
SASESelf Amplified Stimulated Emission
HGHG High Gain Harmonic Generation
Seeding
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Light interacting with an electron beam
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Making E and v parallell
Undulator (or wiggler)
?5 cm
SR in harmonics Velocity ? s
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Mixing light, e- and undulator
vs
vx
Ex
v
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Undulator radiation
t1
t2
t3
l0
l0/2
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Energy exchange
E-field
e-
vx
Some e- gain energy Some e- loose energy S 0
lg
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Bunching
Detour lower v Shortcut higher v
-DE
DE
e-
Bunched e- with distance of light wavelength
lg
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Radiator
lg

• Light generated in an undulator
• Coherent
• With harmonics

lg/3
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Amplification
E-field
Phase shift
vx
lg

• All e- loose energy
• E-field gains energy
• S ? 0

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Saturation
E-field
vx
lg

• Overbunching
• Amplification dies off

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CHG - Coherent Harmonic Generation
l lO /i
lO
laser

• i 1, 3, 5, ?
• l ? 100 nm
• coherent

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Resonator FEL

• IR 5-250 mm
• UV ? 200 nm
• Tunable magnet / e- energy
• Mirrors limit

• Storage ring high rep. Rate, stable
• Linac high peak power, unstable

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SASE (Self Amplified Stimulated Emission)

• From noice
• No mirrors (? X-rays)
• Tunable
• Spiky (t and l)

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SEEDING
laser

• Remove instabilities
• CHG with gain HGHG

Monochromator
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FELIX Resonator IR- FEL FOM, Holland
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ELETTRA, Italy Storage ring FEL l gt 190 nm e-
energy 1 GeV
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TTF, Hamburg Tesla Test Facility l 109 nm SASE
FEL
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LCLS, Stanford Linac Coherent Light Source l
1-15 Å 15 GeV SASE FEL
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MAX-lab VUV FEL Seeded SASE FEL l 100-400
nm 500 MeV 300-400 undulator periods
?
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TESLA, Hamburg
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