Ellipsoidal Laser Status & Results
James Good
PITZ Collaboration Meeting
14 Jun 2017
Introduction
Laser system & on-table data
Results
Redesign
Outlook
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 2
Introduction
> Motivation: Further improvement of the electron beam quality by reduction of the
transverse projected beam emittance.
> Main idea: Optimization of the cathode laser pulse shape in order for to minimize the
impact of the space charge on the transverse emittance.
222
SpChRFcath
min :shapelaser cathode SpCh
cylindrical ellipsoidal
temporally
x
Fx px
x
x
Fx px
x
Minimum SC influence on beam emittance
Better longitudinal compression
Reduced beam halo
Less sensitivity to the machine settings
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 3
Photo Injector Test Facility, DESY Zeuthen
> PITZ is a testbench for photoinjector R&D
Gun quads for beam symmetrization
Plasma self-modulation experiments
Photocathode laser pulse shaping
⇒ an important tool for ↓ε
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 4
PITZ setup and original ASTRA simulation parameters
Simulation setup Three different photo cathode laser shapes have been considered in beam simulations:
Longitudinal distribution: Gaussian. Transverse distribution: radial homogeneous
Longitudinal distribution: Flat-top. Transverse distribution: radial homogeneous
Uniformly filled Ellipsoidal distribution
Bunch charge: 1 nC
Gun gradient: 60.58 MV/m corresponding to Pz~6.7 MeV/c beam momentum after the gun
CDS booster starting position: 3.1 m
CDS booster gradient: 19.76 MV/m corresponding to Pz~24 MeV/c final beam momentum
Reference point: EMSY1 (Z=5.74 m) best emittance for 3 profiles with the same bunch length
~7 MeV/c RF gun ~25 MeV/c CDS
booster
Emittance optimization screen:
5.74 m downstream the cathode
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 5
Beam overview for 3 different laser shapes (Zboo=3.1m)
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 6
Technical requirements
Parameter Value Unit Remark
wavelength 255-270 nm 4th harmonic of Nd
micropulse energy 10-12 μJ 1 nC bunch production
from Cs2Te photocathode
pulse train frequency 1 MHz Future goal: 4.5 MHz
pulse train length 0.3 ms Future goal: 0.6 ms
pulse train rep.rate 10 Hz 1,2,5 Hz as an option
micropulse rms duration 6±2 ps Quasi-ellipsoidal
distribution
transverse rms size 0.5±0.25 mm
Photocathode laser Technical requirements
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 7
> Collaborative development w/ IAP, Nihzny Novogord
> Fiber-based Er laser oscillator and Yb amplifiers
> Multi-pass diode pumped disk amplifier with Yb:KGW crystals
> Hamamatsu SLM-based spatio-temporal shapers
> Second and fourth harmonic conversion
> Scanning cross-correlators & spectrograph(s) (diagnostic)
> Installed end 2016, RF: oscillator synchronization late 2016
Simplified Ellipsoidal Laser (ELLA) setup
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 8
Current pulse shaper: Super-Gaussian
> „Generation of flat-top picosecond pulses by coherent pulse stacking in a
multicrystal birefringent filter“, Ingo Will & Guido Klemz Optics Express, Vol. 16, Issue 19, pp. 14922-14937 (2008)
0
0.2
0.4
0.6
0.8
1
0 5 10 15 20 25 30 35
OS
S S
ign
al
(a.u
.)
Time (ps)
0
0.2
0.4
0.6
0.8
1
0 5 10 15 20 25 30 35
OS
S S
ign
al
(a.u
.)
Time (ps)
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 9
1D SLM-based pulse shaping
> Concept: Spectrally separated chirped pulse transversally modulated by
amplitude-phase mask prior to recombination
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 10
2D SLM-based pulse shaping
Source:
Goal:
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 11
2D SLM shaper
Faraday Isolator, polarizer and
90° beam rotation
,),( ,),(),,(),,( xiyi
inout exMeyMyxEyxE
tyxEin ,,
tyxEout ,,Cylindrical lens
Cylindrical lens
Spherical lenses 2
10~
),( xM
),( x
x
y
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 12
> Horizontal bandcut mask to define
SLM center
> Vertical edge mask to find spectral
center
ELLA spatial/spectral calibration
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 13
IR spectrographic reconstruction
> Slit-scan spectrometer
(modified IAP f600 design)
Standard Czerny-Turner layout
Motorized transverse
translation stage w/ slit
20 nm on-camera spectral dispersion
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 14
IR cross-correlation
Pulse interaction in nonlinear crystal
dttItIW213
~
)(~)(2
ttI 13
~ IW
1
2
3
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 15
Beam quality & operational issues
> Poor oscillator pointing/opto-mechanical stability
Constant slow drift (uncertainties w.r.t. Q,pos, mask)
Pockel cell contrast/leakage
> Spectral-temporal comparison
Band-masking ~1030nm removes sidelobe
> Weak shape preservation
UV beam walkoff/smearing
Pump drift
> Synchronization jitter (ΔQ, ΔP)
IR 515 UV
VC2
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 16
µTCA-based synchronization
> 1st successful trial 16th Nov 2016 (20min)
> Short-term test 20th Nov (6h)
1st Synchronized photoelectrons!
> Long-term test 25th Nov
On-table measurements
Humidity dependent
> Many thanks to:
M. Felber, T .Kozak, H. Schlarb,
G. Schlesselman, F. Tonisch, M. Pohl,
D. Melkumyan, D. Kalantaryan, G. Trowitzsch,
…, …
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 17
ELLA spectral masking (~100 pC)
~13 ps
~13 ps
unshaped
spectrally masked
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 18
ELLA Spectral masking
BSA1.2mm
100 pC
~8 ps
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 19
ELLA 3D ‘FT’ shaping (~200 pC & 500 pC)
200 pC
8 ps
500 pC
15 ps
Nominal BSA: 1.2mm, 0.5nC
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 20
ASTRA simulations for 0.5nC
Ph
oto
cath
od
e laser
Pulse shape
Temporal profile
cylindrical ellipsoid
Gaussian Flattop Homogeneous
ellipsoid
length (FWHM) 9.5 ps
Transverse Homogeneous radial Homogeneous
ellipsoid
Transverse size (rms) 0.385 mm 0.423 mm 0.353 mm
RF
gu
n
Electric field at the cathode (max) 60 MV/m
Phase (w.r.t. MMMG) -1.2° -4.2° -2.8°
Solenoid peak field -0.2247 T -0.2248 T -0.2260 T
Bo
ost
er
Electric field (max) 17.1 МV/m
Phase (w.r.t. MMMG) 0°
Ele
ctr
on
beam
(z=
5.2
77m
)
Bunch charge 0.5 nC
Beam mean momentum 21.0 MeV/c
Projected normalized emittance 0.80 mm·mrad 0.64 mm·mrad 0.35 mm·mrad
Average slice emittance 0.49 mm·mrad 0.57 mm·mrad 0.33 mm·mrad
Bunch length (rms) 1.44 mm 1.20 mm 1.34 mm
Peak current 35.4 А 39.5 А 37.8 А
Longitudinal emittance 34 mm keV 22 mm keV 12.5 mm keV
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 21
ELLA 2.0 reDesign
> Overall goal:
Design & construct a simplified, reliable,
and robust photocathode laser system
Avoid & correct original design
constraints, flaws, and errors
> Design goals:
Minimalized, simplified layout: 50%
reduction of optical elements & path
length (50m → 25m)
modularized & mechanically robust
improved thermal robustness & opto-
mechanical stability
Maximize mask usage & resolution,
minimize AOI
→ lower thermal load & LIDT risk
Uni-directional layout design
→ Independent transverse masks
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 22
> Design considerations:
Future phase masking? Transverse
masking?
Green cathodes/pulse
shaping/characterization?
Volume Bragg gratings
Asymmetric pulse envelopes?
ELLA 2.0 reDesign
SLM
SLM
expander
dove
> Pharos laser properties:
high power 20W, water-cooled, solid state
laser → energy budget up to 100uJ/pulse
variable rep. rate (1 kHz – 1 MHz)
thermo-mechanically stable & optically
flexible
→ SHG and FHG module included
→ Gaussian pulses at variable
pulse duration (0.3 – 15 ps)
Already delivered & installed
→ Synchronization/stability tests
next week(s)
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 23
µTCA-based synchronization
> 72.222MHz Oscillator
Fine tuning: 40Hz/~80V
Coarse tuning: 1.5kHz/80V
Mechanical tuning: 40kHz
> 1st successful trial 8th Jun 2017 (24h)
> Short-term test 9th – 12th Jun (~60h)
Mechanical settling pulled osc.
out of range (Δf = 2.5kHz)
> Continued tests
LEDA check next week?
uTCA phase shifter test?
> No baseline jitter or
de-sync (uTCA timeout fix?)
> Many thanks to:
T .Kozak, F. Tonisch, R. Netzel…
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 24
Summary & Outlook
> Summary
New photocathode laser
design implemented and
utilized
Significant experience gained
in 3D pulse shaping
Successful electron beam
measurements taken
Substantial technical
limitations, constraints &
issues identified
(synchronization, drift, beam
quality, etc.)
>Outlook
New core Pharos laser
system delivered & installed
Sucessful synchronization!
Momentum check next week
New linear optical beam
shaping design finalized &
components ordered
40m → 10m!
Construction begins Jul
New volume Bragg grating
experiments to produce full,
static ellipsoidal distributions
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 25
Thank you for your attention!!!
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 26
Backup slides
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 27
IR 2D reconstruction
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 28
Fiber part
D=1.5mm
Spherical Mirror 2
Spherical Mirror 1
Yb:KGW 1 2f
f
f
Yb:KGW
1
Spherical Mirror
1
Spherical Mirror 2
Yb:KGW
2 Yb:KGW 2
DESIGN OF THE AMPLIFIER
SM 1 SM 2
Yb:KGW 1
(5V passes x 2)
830 mm
Yb:KGW 2
(4V passes x 2)
Transversal
distribution
at the image plane: At the input
After the 1st pass
of the amplifier ( ̴16 m
propagation)
After the 2nd pass
of the amplifier
( ̴32 m
propagation)
Imaging longitudinal accuracy at the output < 10 mm
(22 mm needed) Astigmatism compensating
scheme
Yb:KGW
active
elements:
3% doping level
8.5x8.5x3 mm
disks
6.5% cold losses
per 1V pass
0.22%
depolarization
per 1V pass MULTIPASS
BROADBAND
Yb:KGW AMPLIFIER
FOR 3DESP LASER
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 30
10~
),( xM
),( x
x
y
Faraday Isolator, polarizer and
90° beam rotation
Spherical lenses
Cylindrical lens
Cylindrical lens
The optical scheme allows changing
amplitude and phase of spectral
components
Hamamatsu SLM
800 x 600
liquid crystal phase
modulator
λ
2
,),( ,),(),,(),,( xiyi
inout exMeyMyxEyxE
2D SLM-based pulse shaping
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 31
> Laser controller unit failure (fixed by IAP)
> Water cooling system issues
> All non-linear crystals replaced (incl. amplifier,
cross-correlators, & frequency conversion)
Mar: Yb:KGW amplifier crystals replaced,
frequency conversion crystals & mounts replaced
Apr: IR cross-correlator crystal & mount replaced
> Imperfect laser pointing stability
> Oscillator frequency modulation & locking
Imperfect due to piezo-eigenmodes
> Pump laser cooling circuit pressure spikes
> Holoeye SLM asynchronousity
Unforeseen technical issues
Realtime (ms) Holoeye SLM amplitude trace
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 32
Ch2 instabilities
> Significant energy jitter for maximum power Ch2 observed
Record Ch2 PD traces
Linear fit of peaks & scatter plot of fit coefficients
> Jitter reduction for reduced power
0 100 200 300 400 500 600 700 800-0.02
-0.01
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
Ch2 energy fit spread
Fit slope [/V.s-1]
Fit
off
set
[/V
]
50% Ipeak
100% Ipeak
0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4
x 10-4
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
Time [/s]
Vo
ltag
e [
/V]
CH2 photodiode trace
PD trace
peak detection
linear fit
missing
pulses
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 33
Summary of electron beam parameters for 1nC ASTRA
simulations
James Good | Ellipsoidal Laser Status & Results | 14.06.2017 | Page 34
MBI long-Gauss (15ps) 500 pC emittance
20.01.2017 12:06
Mikhail, Y. Chen
With similar gun & laser setup