helmholtz gemeinschaft vuv fel eo systems at the desy vuv-fel stefan düsterer for the vuv - fel...
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HELMHOLTZ GEMEINSCHAFT VUV FEL
EO systems at the DESY VUV-FELEO systems at the DESY VUV-FEL
Stefan Düsterer
for the VUV - FEL TeamF. Van den Berghe, J. Feldhaus, J. Hauschildt, R. Ischebeck, K. Ludwig, H. Schlarb, B. Schmidt, S. Schmüser, S. Simrock, B. Steffen, A. Winter
and all the others
Adrian Cavalieri, David Fritz, Soo-Heyong Lee, David Reis (Michigan University Ann Arbor, Michigan)
HELMHOLTZ GEMEINSCHAFT VUV FEL
The 2 EOS systemsThe 2 EOS systems
Experiments
EOSEOS
„Electro Optical Sampling“
chirped laser pulse
EOSEOS
„Electro Optical Sampling“
chirped laser pulse
TiSa
fs-oscillator
TEOTEO
„Timing Electro Optical sampling“
45° - geometry
TEOTEO
„Timing Electro Optical sampling“
45° - geometry
pump-probe fs-laser
for FEL-experiments
HELMHOLTZ GEMEINSCHAFT VUV FEL
TTimingimingEOEO
Timing monitor for the FEL-optical pump-probe Experiments
•optimized for electron bunch ARRIVAL TIME measurements
•part of the pump-probe laser system
•final goal:final goal: provide timing data to users
delaydelay + jitter
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Layout: pump-probe experimentsLayout: pump-probe experiments
opticallaser
FEL pulseFEL pulse
Optical pulseOptical pulse
to TEO
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TEOTEO
FEL beam Experim ent
Am plifier
fs-laser oscilla tor(50 fs, 3 nJ, 800 nm ) Optical diode
Feedback signal for changes in fiber length
Grating com pressor:com pensation for first order dispersion
Pulse shaper:Higher order com pensation
Fiber lengthcom pensation
150 m long glass fiberto transport laser pulsesinto the accelerator tunnel
Pockelscell:Pulses needed for E OS can pass- the others are reflec ted provid ing signal for the fiber length stabilization
150 m to experiment
UndulatorLinac
Am
plifi
ed la
ser
beam
(150
fs,1
00µJ
, 800
nm
)
30 m
to e
xper
imen
t
Com pressor + pulse shaper + 150 m glass fiberhave
laser pulses after the fiber are short againtogether no dispersion:
puls length: 50 fs(~ 0.3 nJ)
Electrons
CCD
ZnTe crystal= actual EO-sam pling
Pockels cell
50 % beam splitter
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The laser hutchThe laser hutch
overview picture - CDR layout
TEO
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The TEO layout - in the laser hutchThe TEO layout - in the laser hutch
laser hutch - CDR layout
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The TEO layout - in the tunnelThe TEO layout - in the tunnel
tunnel - CDR layoutHigh degree of automation
19 motors 19 motors
6 cameras 6 cameras
3 photo diodes / PMTs3 photo diodes / PMTs
every important parameter can be
controlled and changed
from the control room
- fully integrated in the control system -- fully integrated in the control system -
High degree of automation
19 motors 19 motors
6 cameras 6 cameras
3 photo diodes / PMTs3 photo diodes / PMTs
every important parameter can be
controlled and changed
from the control room
- fully integrated in the control system -- fully integrated in the control system -
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TEO - first steps...TEO - first steps...
Laser hutch
Accelerator tunnel
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TEO - simulationsTEO - simulations
critical parts like
the compressorthe compressor
the phase-shaperthe phase-shaper
the imaging of the crystalthe imaging of the crystal
the interaction between laser and el. field in the crystalthe interaction between laser and el. field in the crystal
were simulated in order to optimize TEOs performance
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introducing LAB II simulation softwareintroducing LAB II simulation software
Simulation of fs-pulse propagation by Th. Feurer and groupTh. Feurer and group (Jena / MIT /Bern)
time - frequency domain (no spatial calculations)
linear and nonlinear effects / three wave mixing
various materials
compressors, strechers and phase shaper
auto- / cross-correlation, FROGs
and much much more
Based on LabView
Free download at
Free download at
www.lab2.de
www.lab2.de
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Lab II - simulation of TEOLab II - simulation of TEO
~ 70 fs FWHM
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The compressorThe compressor
compensate for dispersion induced fs-pulse broadening by the 170 m glass fiber
compensates the huge Group Velocity Dispersion (GVD)
(second order deriv. of phase)
BUT induces third (and higher) order phase distortions (TOD)
optimization dilemma bandwidth transmission (constant grating size)
induced TOD
highly dispersive gratings
(1800 lines / mm) low dispersive gratings
(1200 lines / mm)
TOD induced by fiber: 0.5 107 fs3 / TOD by compressor: 1-2 107 fs3
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the phase shaper - actual designthe phase shaper - actual design
Geometry is entirely on-axis. ( design by G. Stobrawa, U. Jena)
folding mirror
algorithms for LCD-matrix
- start with genetic algorithm (Soo / Michigan)
-next step:
parameterization with to Taylor coefficients . of the phase (about 100 times faster - Jena)
algorithms for LCD-matrix
- start with genetic algorithm (Soo / Michigan)
-next step:
parameterization with to Taylor coefficients . of the phase (about 100 times faster - Jena)
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TEO - imagingTEO - imaging
ray tracing well below diffraction limit
wave front propagation
1:2 imaging
using achromatic lenses
Tilted object → tilted camera
diffraction limited resolution diffraction limited resolution
< 10 µm < 10 µm
for 2 mm field of view
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0.5mm
10mm
The wedged crystal The wedged crystal (ZnTe)(ZnTe)
Signal Temporal resolution
Thick crystal Thin crystal
Change sensitivity vs. temporal resolution online online
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Wedged crystalWedged crystal
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Simulation of EO-Response FunctionSimulation of EO-Response Function
First reflectionof THz field e-beam
Linear diode array1000 pixel
• incidence angle of laser• freq. dependent refraction• freq. dependent EO-coeff.• group velocity mismatch• multiple reflection
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Simulation of EO-Response FunctionSimulation of EO-Response Function
T=-50 fs
20% shorter bunch
5% more charge
origin
100 pixel
17%
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Challenge: detection at 1 MHz
ELIS photo-diode array (silicon video inc.):
Pixels: 1024 / 8 µm Readout: 30 MHz
1000 pixel -> 30 µs 128 pixel -> 4 µs
Gating 15 ns
Low cost ns
15 ns
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Differences between TEO and SPPSDifferences between TEO and SPPS
Pockels cell behind fs-oscillator ~ 100% of laser power available
all reflective shaper
70 fs pulses (FWHM) at crystal are possible
60 nm transmission through the whole system
jitter: no regenerative laser amplifier - but larger distance to experiment
gating by detection (line camera)
wedge crystalwedge crystal – change temporal resolution continuously and online
More than 20 motors / 6 cameras – TEO can be entirely remote controlled More than 20 motors / 6 cameras – TEO can be entirely remote controlled
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EOSEOS
Timing monitor for the FEL-optical pump-probe Experiments
• Flexible EOS system to test various concepts
•scanning EO
•chirped pulse EO
• Electron bunch diagnosticElectron bunch diagnostic
•longitudinal bunch structure
Sub 15 fs Femtolaser
Located in container close to the accelerator
15 m beamline (future upgrade: amplified pulse / single shot correlation)
Container electrically isolated / RF shielding
Temperature stabilized RF cable
Beamline for CTR -> EOS in container ( test of crystals …)
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EOS - SetupEOS - Setup
To spectrometerOTR
ZnTe crystal
300 µm
electrons
TiSa fs pulse
65 nm FWHM / 15 fs
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ConclusionConclusion
• 2 EOS systems 2 EOS systems – to test different EO schemes – Cross-check
• (Goal) Measure at 1 MHz – each pulse – Machine diagnostics– Essential for user pump-probe experiments
• TEO– 50 fs arrival time monitor– Highly automated (standard diagnostics)
• EOS– 100 fs longitudinal electron bunch resolution
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Dies ist eine Dies ist eine
schöne vorlage ...
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TEO in numbersTEO in numbers
shaper:shaper:
• 640 element LCD matrix, 1800 l/mm grating , 500 mm focal distance
•wavelength transmission: 800 +- 30 nm
•TOD compensation = 1.2 107 fs3
compressor:compressor:
• 1500 l/mm gratings / 140 mm wide / 1.2m separation
•wavelength transmission: 800 +- 30 nm
•TOD induced = 1.4 107 fs3
fiber:fiber:
•170 m long
•Single mode polarization maintaining
•TOD induced = 0.5 107 fs3
• cutoff wavelength < 780 nm
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Er
Principal ofelectro-optical
samplingPD
Sampling:• simple analysis• balanced detector allows high sensitivity• good synchronization required• multi-shot method• arbitrary time window possible
Er
Principal oftemporal-
wavelength correlationcamera
Chirp laser method:• single shot method• some more effort for laser and laser diagnostics required • resolution due to laser ~ √t0· tchirp • time window ~ 1-20ps
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Space -time correlation methodSpace -time correlation method
Timing o.k.Timing o.k.
EO-Crystal
v
Er
camera
v
laser is „late“laser is „late“
v
laser is „early“laser is „early“
laser
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the phase shaper - principlethe phase shaper - principle
actual shaper
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Time structure and energy budgetTime structure and energy budget
Ti:Sa oscillator pulses
fiber
108 MHz
OPA
SHG10%
PM
0.01%
Pockels cell 1 MHz
Rotator
SHG
92%
5%
91%
stretcher
SLM
~ 800 ns
t = 1600 ns
9.3 ns
1 MHz
tunnel
t = 0 ns
gated detectorEO-crystal
e-bunch
0.6%
10%
90%
X 1000
0.6%0.6%
~ 800 ns
~ 1600 ns
Synchronized to electron beam at EO-crystal
Synchronized to VUV-FEL beam at sample
Pulse for SHG sampling the fiber length
Pulse for SHG for reference
50%
50%
50%
50%
92%
130 pJ
2.5 nJ
90%
10%
2*40 pJ
15 pJ
98%
FeedbackFiber length
Pump-probe experiment
PM