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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)
Mikhail Krasilnikov | Cathode Laser Pulse Shaping For High Brightness Electron Sources | FLS 2012, 6.03.2012 | Page 3
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
Mikhail Krasilnikov | Cathode Laser Pulse Shaping For High Brightness Electron Sources | FLS 2012, 6.03.2012 | Page 4
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
12.04.2011, 0.1nC-optimization
30.04.2011, 0.02nC-optimization
FWHM=(21.20
0.33)ps
rise time=(2.02
0.11)ps
fall time=(2.62
0.13)ps
Mikhail Krasilnikov | Cathode Laser Pulse Shaping For High Brightness Electron Sources | FLS 2012, 6.03.2012 | Page 5
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)
Mikhail Krasilnikov | Cathode Laser Pulse Shaping For High Brightness Electron Sources | FLS 2012, 6.03.2012 | Page 6
-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%
Temporal laser shapes
used for the simulation
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%
Temporal laser shapes
used for the simulation
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%
Temporal laser shapes
used for the simulation
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
Mikhail Krasilnikov | Cathode Laser Pulse Shaping For High Brightness Electron Sources | FLS 2012, 6.03.2012 | Page 7
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
3 peaks on crest +6 deg
4 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
Mikhail Krasilnikov | Cathode Laser Pulse Shaping For High Brightness Electron Sources | FLS 2012, 6.03.2012 | Page 8
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)
Mikhail Krasilnikov | Cathode Laser Pulse Shaping For High Brightness Electron Sources | FLS 2012, 6.03.2012 | Page 9
• 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
Mikhail Krasilnikov | Cathode Laser Pulse Shaping For High Brightness Electron Sources | FLS 2012, 6.03.2012 | Page 10
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
Mikhail Krasilnikov | Cathode Laser Pulse Shaping For High Brightness Electron Sources | FLS 2012, 6.03.2012 | Page 11
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)
Mikhail Krasilnikov | Cathode Laser Pulse Shaping For High Brightness Electron Sources | FLS 2012, 6.03.2012 | Page 12
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
Mikhail Krasilnikov | Cathode Laser Pulse Shaping For High Brightness Electron Sources | FLS 2012, 6.03.2012 | Page 13
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
Mikhail Krasilnikov | Cathode Laser Pulse Shaping For High Brightness Electron Sources | FLS 2012, 6.03.2012 | Page 14
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%
Gaussian flat-top Ellipsoid
rel.e
mitt
an
ce
Electron beam transverse distribution at z=5.74m
Mikhail Krasilnikov | Cathode Laser Pulse Shaping For High Brightness Electron Sources | FLS 2012, 6.03.2012 | Page 15
BD simulations for bunch charge 1 nC Projected emittance (1nC) at EMSY1
168%
100%65%
0%
50%
100%
150%
Gaussian flat-top Ellipsoid
rel.e
mitta
nce
Electron beam (Z-X) shape at z=5.74m
Longitudinal phase space (Z-Pz) at z=5.74m
less nonlinearity
Mikhail Krasilnikov | Cathode Laser Pulse Shaping For High Brightness Electron Sources | FLS 2012, 6.03.2012 | Page 16
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