Single-shot, Sub-picosecond, EO bunch measurements at FELIX

Steven Jamison, Giel Berden, Allan MacLeodAllan Gillespie, Jingling Shen, Dino Jaroszynski,

Britta Redlich, Lex van der Meer

School of Computing and Advanced Technologies, University of Abertay, Dundee, UKDepartment of Physics, University of Strathclyde, Glasgow, UK

FOM Institute for Plasma Physics “Rijnhuizen”, Nieuwegein, The Netherlands

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 2

• Single-shot electro-optic detection of ultra-short bunches

- spectral-decoding- temporal decoding

• FELIX electron bunch measurementsreal time bunch profile adjustmentbunch timing jittercharge dependence

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 3

Electro-optic detection of Coulomb field:

Temporal decoding method

Spectral decoding method

450fs

1.7ps

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 4

;0for ; )()( )()( d )()( 0

Coul

INOpt

*Coul

INOpt

INCoul

INOpt

EEEEEE

Mixing of optical spectrum with neighbouring frequencies

Time-resolution of spectral decoding.

)( )( )( Coul21INOpt

OUTOpt tEaatEtE

)ω()ω( )( )ω( CoulINOpt2

INOpt1

OUTOpt EEaEaE

Time domain

Frequency domainFouriertransform

approximate temporal limitation based on bandwidth

C 0b. ~

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 5

)4//cos()()( 20

2

tEE Coulopt

)()( )( )(22

Couloptopt EEES

) -(2 where 0

Time-resolution function NOT a smoothing function. Can cause artifacts!!

Should be considered as temporal limitation

e.g balanced detection: measure change in probe spectrum…

spectrumGaussian for ; 2.6

generalin ; 12

0 Ctt

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 6

Multi-shot scanning optical delay

Lab-bench test-bed for EO techniques

Single-shot spectral decoding

able to produce mimic of Coulomb field with unipolar THz pulse from GaAs emitter

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 7

Observe oscillating features on shorter time scale than usual “time resolution”

Jamison et al. Opt. Lett. 18 1710 (2003)

4

cos)( 2

0

tECoul

)( CoulE

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 8

Temporal decoding

• Same chirped pulse encoding of Coulomb field information.

• Decode information through time-domain measurement of probe intensity

)( )( )( Coul21INOpt

OUTOpt tEaatEtE

Cross-correlation of EO modulated pulse, IOpt(t) ~ EOpt2(t)

with transform limited “gate” pulse, Igate(t)

d )( )( d )( )( )( ~

d )( )( ~ )(

gateINOpt

2gate

INOptCoul21

gateOUTOpt

1tItIatItItEaa

tItItS

Time resolution set by gate pulse duration (<50fs)

(balanced detection example)

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 9

Chirped probe focussed on ZnTe in beamline (sampling field at single point)

Probe expanded and collimated forcross-correlator

(for temporal-spatial mapping)

Temporal decoding at FELIX

~100J 30 fs

~1J 21 ps

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 10

30-50MeV electron beam measurements FELIX FEL facility, Rijnhuizen, Netherlands

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 11

Time window, :•Beam diameter, D•Angle of incidence

cD /)sin(2

ps for D=5mm,

Phase matching in BBO achievable for incident angles o

Second-harmonic generation (single shot) cross-correlation

Symmetric crystal geometry: 400nm walk-off orthogonal to

time-axisAble to choose time window from fs → 30ps for 1cm beam (outside beamline!)

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 12

Temporal profile of probe pulse → Spatial image of SHG

Single-shot “temporal decoding” of optical probe

Symmetrical optical arrangement

No temporal blurring with crystal thickness

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 13

FELIX FEL facility, Rijnhuizen, Netherlands

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 14

5mm

Electron bunch

Chirped probe pulse

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 15

ZnTe Reflection geometry….

High frequency signal components• cancel during counter-propagating path

• sampled during co-propagating path

Low frequency components• “averaged” during counter-

propagating path

• sampled during co-propagating path

doubled retardation

EO without any upstream mirror …

Have applied this technique to single-shot laser-plasma EO bunch measurements (May & August 2003)

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 16

~800fs

~600fs

30MeV→110fs resolution (at 1mm from beam)

28 July, 2003

Berden et al.Proceedings of FEL2003

Early temporal decoding measurements at FELIX (July 2003)

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 17

Temporal decoding measurements at FELIXDecember 2003

450fs FWHM

G. Berden, S.P. Jamison et al. Accepted for Phys. Rev. Lett.

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 18

Bunch timing jitter

Temporal decoding measurements at FELIXDecember 2003

Bunch profile versus EO signal…

“Crossed-polarisers”

•Zero background signal

•Signal ~ E2

“Balanced detection”•Small modulation on large background

•Signal ~ E

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 20

Ecoulomb = [EO signal]1/2

Quadratic dependence of EO signal on field confirmed by varying bunch charge ( EO signal Q2 )

Using “crossed-polariser” configuration EO signal [Coulomb Field]2

Determining Coulomb field from EO signal

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 21

Confirmation of time-resolution and quadratic EO dependence with monochromatic FEL radiation

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 22

4

sin)(

4cos)( )(

22

0

22

0SD

tE

tES

Coul

Coul

)( )( TD tSECoul

)(TD tS

temporal decoding measurement NOT time-resolution limited

Temporal decoding, spectral decoding comparison

(crossed polarisers configuration)

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 23

Real time beam adjustment(beam-steering towards crystal)

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 24

Real time monitoring and bunch profile modification…

Bunch profile modified by changing the buncher and

accelerator phase.

. 450 fs FWHMCoulomb field on sub peak

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 25

Alternative EO materials. (GaP, GaSe, DAST…)Approximate interpolation…

~30fs possible (?)

>300fs bunch duration limitation Solved by temporal decoding ~30-50fs possible

>200fs limitation for undistorted measurementRigorous retrieval of true field possible

Spectrum-envelope interdependence (spectral-decoding)

EO crystal absorption

EO phase matching

Optical bandwidth Time resolution approx. optical pulse duration. ~30 fs. Improvements through X-FROG, ….?

Need even better time-resolution…. (measuring sub-200fs bunches) .

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 26

• CONCLUSIONS FOR TEMPORAL DECODING…..

• Demonstrated non-destructive longitudinal profile measurement with 650fs FWHM bunches

• ~450fs FWHM substructure observed

• Estimated time resolution ~300fs (2.8THz), due to ZnTe response and low of bunch

• Real-time bunch shape monitoring and adjustment

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004 27

Jingling Shen Dino Jaroszynski

Giel BerdenBritta RedlichLex van der Meer

Allan MacLeodAllan GillespieSteve Jamison

Supported by EPSRC Basic Technology Programme (alpha-X project on wavefield accelerator driven FEL)

(Capital Normal University, Beijing)