LC-ABDP.J. Phillips, W.A. Gillespie (University of Dundee)

S. P. Jamison (ASTeC, Daresbury Laboratory)A.M. Macleod (University of Abertay)

CollaboratorsG. Berden, A.F.G. van der Meer (FELIX)

B. Steffen, E.-A. Knabbe, H. Schlarb, B. Schmidt,P. Schmüser (DESY)

Electro-optic characterisation of bunch longitudinal profile

Why do we need an ultra-fast electron bunch diagnostic?

Machine operation has high influence on beam shape

Wakefields

Synchrotron radiation

Beam – Beam interaction

Electro-optic longitudinal bunch profile measurements

~ ETHz

Propagating electric field

Effective polarisation rotation proportional to Coulomb field

Convert bunch Coulomb field into optical intensity variation.Coulomb field encoded

into optical probeDecoding: temporal intensity variations in single laser pulse

e-bunch

- 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

Temporal Decoding

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

ZnTe GaP

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

Theoretical (but based on some experimental data)

Experimental setup at the VUV-FEL

the laser system is housed outside the accelerator tunnel including 4 nJ, 15 fs Ti:Sa oscillator 1 mJ, 30 fs Ti:Sa 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

Resulting e-bunches at 450 MeV with 1000 pC in a < 100 fs spike during FEL operation at 32 nm.

Laser Hutch at FLASH

Temporal Decoding

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15time [ps]

EO

sig

na

l

)(80 rmsfs

Benchmarking EO by LOLA450 MeV, 1nC~20% charge in main peak

January-February 2007 results...

Electro-optic bunch profile

Transverse Deflecting Cavity bunch profile (LOLA)

)(80 rmsfs

probe laser

bunch

gate laser

Time Calibration....

The measured retardationCalculated electric fieldSimulated EO signal / phase retardationMeasured LOLA signal

Data taken with GaP (175 um)Q=0.84 nC, r = 3.8 mm; LOLA Res 3.2 fs /pix

Current data taken at FLASH

Simulation by B. Steffen

For a fitted Gaussian curve we get a of 80 fs +/- 8fs rms

Can we get shorter resolution

• Lola measurement Actual bunch profile (10 fs resolution)

• Coulomb angle 1/~ 50 fs for ~ 1000

• Material– GaP

– New material ( Phase matching, 2

considerations)

• Gate pulse width ~ 50 fs– Introduce shorter pulse

– Spectral interferometry

– FROG Measurement

– Try these methods on ERLP

)(80 rmsfs

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 al2 EPAC 2006 A. Winter et al

Fibre Laser

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 Ti:Sapphire (SHG of Fibre laser ?) knowledge to amplified laser system

Conclusions

• Achieved success at FELIX, DESY

• Measured an Electron Bunch spike at ~ 80 fs (rms)

• Wish to do measurements at SLAC