Cathode Laser Pulse Shaping For High Brightness Electron ...€¦ · Cathode Laser Pulse Shaping...

Cathode Laser Pulse Shaping For High Brightness Electron Sources

(PITZ Experience) Mikhail Krasilnikov (DESY) for the PITZ Team

Content:

• Photo cathode laser system at PITZ

• Temporal pulse shaping – flat-top profile:

• rise/fall time impact

• flat-top modulations studies

• Transverse laser distribution influence

• Advanced pulse shaping of the cathode laser: 3D ellipsoid

• Summary

ICFA Workshop on Future Light Sources, March 5-9, 2012

Thomas Jefferson National Accelerator Facility, Newport News, VA

Mikhail Krasilnikov | Cathode Laser Pulse Shaping For High Brightness Electron Sources | FLS 2012, 6.03.2012 | Page 2

Yb:YAG laser at PITZ with integrated optical sampling system

Two-stage Yb:YAG

double-pass amplifier

G ~ 40

Emicro=

0.002 mJ

Emicro~

80 mJ

Emicro=

0.002 mJ

Emicro~

2 mJ

LBO BBO

UV output

pulses

Emicro~

10 mJ

Optical Sampling System

(OSS)

scanning

amplifier

(Yb:KGW) Yb:YAG power regen

G ~ 106

Pulse

selector

pulse

shaper

Highly-stable

Yb:YAG

oscillator

pulse

selector Nonlinear

fiber

amplifier Resolution: t < 0.5…1 ps

t ~ 1.7 ps

PITZ Photo cathode laser (Max-Born-Institute, Berlin)


Multicrystal birefringent pulse shaper containing 13 crystals

FWHM

= 25 ps edge10-90

~ 2.2 ps

edge10-90

~ 2 ps

birefringent shaper, 13 crystals

OSS signal (UV)

temperature

controlled

birefringent

crystal

motorized

rotation

stage

Gaussian

input

pulses

Shaped

ouput

pulses

Will, Klemz, Optics Express

16 (2008) , 4922-14935

Photo cathode laser: temporal pulse shaping


Photo cathode laser: flat-top temporal pulse profiles

Laser temporal profile used for the emittance optimization at various bunch charge levels

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

-14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14

no

rm. la

se

r in

ten

sity,

a.u

.

t, ps

02.05.2011, 2nC-optimization

07.05.2011, 1nC-optimization

12.04.2011, 0.25nC-optimization



FWHM=(21.20

0.33)ps

rise time=(2.02

0.11)ps

fall time=(2.62

0.13)ps


0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

1.6

2 3 4 5 6 7

rise/fall time, ps

em

itt, m

m m

rad

measured XY-emittance

simulated XY-emittance

Check effect on rise/fall time – results of 2009

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

1.6

2 3 4 5 6 7rise/fall time, ps

em

itt, m

m m

rad

EmX

EmY

•Q=1nC

•Imainoptimized

•Gun: +6deg off-crest

•Booster: on-crest

•Laser: temp FWHM~20ps, BSA=1.5mm

• In 2009 it was not possible to measure the effect

with current machine stability

•After the improvement of the phase stability the

effect is planned to be rechecked (this year)

Best measurements

(22.08.2009M)

http://pitzlb.ifh.de:8080/PITZelog/data/2009/37/09.09_a/2009-09-09T21:12:11-00.ps


http://pitzlb.ifh.de:8080/PITZelog/data/2009/37/10.09_M/2009-09-10T10:09:33-00.ps


-18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

Temporal laser shapes

used for the simulation

flat top

5 %

10 %

20 %

30 %

40 %

50 %

75 %

100%

inte

nsity, Q

no

rm.

time, ps

-18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

flat top

5 %

10 %

20 %

30 %

40 %

50 %

75 %

100%



inte

nsity, Q

no

rm.

time, ps

-18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

flat top

5 %

10 %

20 %

30 %

40 %

50 %

75 %

100%



inte

nsity, Q

no

rm.

time, ps

-18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

flat top

5 %

10 %

20 %

30 %

40 %

50 %

75 %

100%



inte

nsity, Q

no

rm.

time, ps

Various laser temporal flat-top modulations Simulations

0,0 0,2 0,4 0,6 0,8 1,0

0,60

0,65

0,70

0,75

0,80

0,85

0,90

0,95

1,00

1,05

1,10

1,15

1,20

2 peaks

3 peaks

4 peaks

5 peaks

em

itta

nce

(m

m m

rad

)

modulation depth

0

10

20

30

40

50

60

70

80

Simulated optimum emittance vs.

modulation depth

em

itta

nce

ch

an

ge

(%

)

• higher modulation frequency larger emittance growth rate

• reliable simulations for modulations with >5 peaks are difficult

simulations with

gun on-crest,

other parameters

optimized

2 peaks

3 peaks

4 peaks

5 peaks


Laser temporal profile modulations Experiment: measurements in 2009

0 20 40 60 80 100

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

2,2simulation

2 peaks 3 peaks 4 peaks

experiment

2 peaks on crest +6 deg



em

itta

nce

(m

m m

rad

)

modulation depth (%)

Experimental results compared to simulations

2 peaks

3 peaks

4 peaks

default

In 2009 it was not possible to measure the

effect with the current machine stability

http://pitzlb.ifh.de:8080/PITZelog/data/2009/33/13.08_n/2009-08-14T01:25:39-00.ps











Measurements with / without modulations on the temporal laser distribution

with modulations without modulations

Approach detuning of an aligned pulse shaper, i.e. by purpose introducing

modulations on the flat-top of the temporal laser distribution and measuring momentum

distribution in HEDA

Laser temporal

profiles

Electron beam

longitudinal

momentum

distribution

Electron beam

longitudinal

momentum

distribution

Machine conditions:

gun: on-crest

booster: +10deg off-crest

bunch charge: 500pC

(5 laser pulses used) (1 laser pulse used)


• Resonantly driven plasma wave

high tranformation ratio

5 Bunchlets inside the bunch:

Studies for Particle Driven Plasma Acceleration @PITZ

• Self-modulation without seed

but with flat-top modulation:

• Self-modulation

with seed pulse:

to be sent

to bunch

compres-

sor

mradmmxy 448.0

mradmmxy 471.0

,45.48 mxy m

,25.83 mxy m

mmz 311.0

mmLb 05.4,50pCQ

,10pCQ

Flat-top:

Gauss:

123

1 1069.3][ cmnb

133

2 1005.1][ cmnb

1bn2bn

Photo cathode laser

distributions

Output parameters for 2 sub-bunches @6.28m from cathode:

probe

bunch

V

V


Photo cathode laser: transverse pulse shaping

laser spot at

“virtual cathode”

Beam Shaping Aperture (BSA)

plate is now replaced by an iris

with remotely tunable opening

imaging of the BSA onto the

photo cathode

laser beam

steering



Photo cathode laser: transverse distributions

BSA=1.2mm (1nC)

RMS sizes (no Gaussian fit!)

x=0.30 mm and y=0.29 mm

RMS sizes (no Gaussian fit!)

x=0.13 mm and y=0.12 mm

BSA=0.5mm (0.1nC)


Laser pulse shaping studies for further improvement of the

electron beam quality in a photo injector

cylindrical 3D ellipsoidal

temporally Gaussian

(e.g. FLASH)

Trms=4.4ps

Flat-top

(e.g PITZ)

FWHM~20ps, rt~2ps

222

SpChRFcath

min :shapelaser cathode SpCh

Beam dynamics (ASTRA)

simulations for PITZ-1.8 setup


BD simulations for bunch charge 1 nC

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 2 4 6 8 10z, m

mm

mra

d

Xemit (Gaussian 4.4ps)

Xemit (flat-top)

Xemit (ellipsoid)

Slice parameters at z=5.74m

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

-6 -4 -2 0 2 4 6z-<z>, mm

sl.

em

itta

nce,

mm

mra

d

0

10

20

30

40

50

60

beam

curr

ent,

A

XYemit (Gaussian, 4.4ps) XYemit (f lat-top)

XYemit (ellipsoid) current (Gaussian 4.4ps)

current (f lat-top) current (ellipsoid)

1.02

0.65

0.42

0.62

0.44

0.34

0.50

0.37

0.29

0.35

0.260.21

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

Trms=4.4ps 20ps/2ps Trms=Trms(f-t)

Gaussian flat-top Ellipsoid

100%

95%

90%

80%

Core emittance

3D ellipsoidal

temporal profile Gaussian Flat-top

transverse distribution

Trms ps 4,4 5,8 5,8

XYrms mm 0,427 0,415 0,389

Ek eV

th.emit. mm mrad 0,36 0,35 0,33

Ecath MV/m

phase deg -3,1 -1,9 -2,8

maxBz T -0,2253 -0,2258 -0,2277

maxE 18,5 19,1 19,1

phase deg

charge nC

energy MeV 22,3 22,7 22,8

proj.emit. mm mrad 1,02 0,65 0,42

th./proj.em. % 36% 54% 78%

<sl.emit.> mm mrad 0,82 0,58 0,41

51 106 270

RF

-gun

3D ellipsoidal

cylindrical

laser shape type

radial homogen.

e-b

eam

@E

MS

Y1

B~Ipeak/em 2̂

1

0CD

S

boost

parameter unit

0,55cath

ode laser

60


14

BD simulations for bunch charge 1 nC

Transverse phase space at z=5.74m

reduced beam halo almost no beam halo

Projected emittance (1nC) at EMSY1

100%

60%39%

0%

20%

40%

60%

80%

100%


rel.e

mitt

an

ce

Electron beam transverse distribution at z=5.74m


BD simulations for bunch charge 1 nC Projected emittance (1nC) at EMSY1

168%

100%65%

0%

50%

100%

150%


rel.e

mitta

nce

Electron beam (Z-X) shape at z=5.74m

Longitudinal phase space (Z-Pz) at z=5.74m

less nonlinearity


Conclusions

> Cathode laser pulse shaping is one of the key parameters for a high

brightness photo injector

> Nominal temporal pulse shape at PITZ – a flat-top of ~ 20ps FWHM

Short rise/fall time, first trials were performed in 2009, to be checked soon

Flat-top modulations: no large impact onto the transverse phase space, but longitudinal

phase space modulations

> Transverse laser distribution:

Laser transport and imaging to the cathode

“Fresh cathode” effect homogeneous emission area

> Beam dynamics simulations applying a 3D pulse shaping (ellipsoid) for the

PITZ injector yield : significant reduction in beam projected and slice emittance

reduced beam halo and less sensitivity to machine parameters

less nonlinear longitudinal phase space

practical realization BMBF project with IAP, Nizhniy Novgorod, Russia

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