LCABD

1
Electro-optic characterisation of bunch
longitudinal profile

• LC-ABD
• P.J. Phillips, W.A. Gillespie (University of
  Dundee)
• S. P. Jamison (ASTeC, Daresbury Laboratory)
• A.M. Macleod (University of Abertay)
• Collaborators
• G. Berden, A.F.G. van der Meer (FELIX)
• B. Steffen, E.-A. Knabbe, H. Schlarb, B. Schmidt,
• P. Schmüser (DESY)

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Why do we need an ultra-fast electron bunch
diagnostic?Machine operation has high influence
on beam shapeWakefieldsSynchrotron
radiationBeam Beam interaction
3
Electro-optic longitudinal bunch profile
measurements
Convert bunch Coulomb field into optical
intensity variation.
Coulomb field encoded into optical probe
Decoding temporal intensity variations in
single laser pulse
e-bunch
Propagating electric field
Effective polarisation rotation proportional to
Coulomb field
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Temporal Decoding

• the chirped laser pulse behind the EO crystal is
  measured by a short laser pulse with a single
  shot cross correlation technique
• approx. 1mJ laser pulse energy necessary

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Encoding Time Resolution... material response,
R(w)

• velocity mismatch of Coulomb field and probe
  laser
• frequency mixing efficiency c (2)(w)

ZnTe
GaP
Theoretical (but based on some experimental data)
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Experimental setup at the VUV-FEL
Resulting e-bunches at 450 MeV with 1000 pC in a
lt 100 fs spike during FEL operation at 32 nm.
the laser system is housed outside the
accelerator tunnel including 4 nJ, 15 fs TiSa
oscillator 1 mJ, 30 fs TiSa amplifier the
laser beam is transported via a 20m vacuum
transfer line current setup allows sampling,
spectral and temporal decoding currently ZnTe
(185µm) and GaP (170µm) crystal mounted
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Laser Hutch at FLASH
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Temporal Decoding
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Benchmarking EO by LOLA
450 MeV, 1nC20 charge in main peak
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January-February 2007 results...
Electro-optic bunch profile
Transverse Deflecting Cavity bunch profile (LOLA)
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Time Calibration....
probe laser
gate laser
bunch
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Current data taken at FLASH
Data taken with GaP (175 um)Q0.84 nC, r 3.8
mm LOLA Res 3.2 fs /pix
The measured retardation Calculated electric
field Simulated EO signal / phase
retardation Measured LOLA signal
Simulation by B. Steffen
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For a fitted Gaussian curve we get a s of 80 fs
/- 8fs rms
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Can we get shorter resolution

• Lola measurement Actual bunch profile (10 fs
  resolution)
• Coulomb angle 1/g 50 fs for g 1000
• Material
• GaP
• New material ( Phase matching, c2 considerations)
• Gate pulse width 50 fs
• Introduce shorter pulse
• Spectral interferometry
• FROG Measurement
• Try these methods on ERLP

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Research into Fibre lasers

• Clock to be distributed by fibre lasers through
  stabilised fibres1
• Synchronisation to experiments in future
  accelerators
• Synchronisation of RF to Laser pulses is
  currently to 30 fs over several hundred meters2
• Inherently low noise

1 FEL 2004 J. Kim et al 2 EPAC 2006 A. Winter et
al
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Fibre Laser
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Our Fibre laser interests

• Fibre system will exist for timing distribution
• Exploit for robust / reliability distribution of
  EO monitors
• Dual function of precision arrival time monitor
• Requires
• Transport of TiSapphire (SHG of Fibre laser ?)
  knowledge to amplified laser system

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Conclusions

• Achieved success at FELIX, DESY
• Measured an Electron Bunch spike at 80 fs
  (rms)
• Wish to do measurements at SLAC