Transcript Duesterer-EO-at

VUV FEL
HELMHOLTZ GEMEINSCHAFT
EO systems at the DESY VUV-FEL
Stefan Düsterer
for the VUV - FEL Team
F. 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)
The 2 EOS systems
VUV FEL
HELMHOLTZ GEMEINSCHAFT
TiSa
pump-probe fs-laser
fs-oscillator
for FEL-experiments
Experiments
EOS
„Electro Optical Sampling“
chirped laser pulse
TEO
„Timing Electro Optical sampling“
45° - geometry
TimingEO
VUV FEL
HELMHOLTZ GEMEINSCHAFT
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: provide timing data to users
delay + jitter
delay
Layout: pump-probe experiments
VUV FEL
HELMHOLTZ GEMEINSCHAFT
FEL pulse
Optical pulse
to TEO
optical
laser
TEO
Compressor + pulse shaper + 150 m glass fiber
together have no dispersion:
laser pulses after the fiber are short again
HELMHOLTZ GEMEINSCHAFT
Pockels cell
fs-laser oscillator
(50 fs, 3 nJ, 800 nm)
Optical diode
Feedback signal
for changes in
fiber length
per
ime
nt
puls length: 50 fs
(~ 0.3 nJ)
50 % beam splitter
CCD
A
Experiment
150 m long glass fiber
to transport laser pulses
into the accelerator tunnel
Pulse shaper:
Higher order
compensation
Fiber length
compensation
m
(15 plified
0 fs
,10 laser
0µJ
, 80 beam
30
0n
mt
m)
oe
x
Amplifier
Grating compressor:
compensation for
first order dispersion
VUV FEL
Pockelscell:
Pulses needed for EOS can pass
- the others are reflected providing
signal for the fiber length stabilization
FEL beam
Electrons
Undulator
ZnTe crystal
= actual EO-sampling
150 m to experiment
Linac
The laser hutch
VUV FEL
HELMHOLTZ GEMEINSCHAFT
TEO
overview picture - CDR layout
The TEO layout - in the laser hutch
VUV FEL
HELMHOLTZ GEMEINSCHAFT
laser hutch - CDR layout
The TEO layout - in the tunnel
VUV FEL
HELMHOLTZ GEMEINSCHAFT
High degree of automation
tunnel - CDR layout
19 motors
6 cameras
3 photo diodes / PMTs
every important parameter can be
controlled and changed
from the control room
- fully integrated in the control system -
TEO - first steps...
VUV FEL
HELMHOLTZ GEMEINSCHAFT
Laser hutch
Accelerator tunnel
TEO - simulations
VUV FEL
HELMHOLTZ GEMEINSCHAFT
critical parts like
the compressor
the phase-shaper
the imaging of the crystal
the interaction between laser and el. field in the crystal
were simulated in order to optimize TEOs performance
HELMHOLTZ GEMEINSCHAFT
introducing LAB II simulation software
VUV FEL
Simulation of fs-pulse propagation by Th. 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
Lab II - simulation of TEO
VUV FEL
HELMHOLTZ GEMEINSCHAFT
~ 70 fs FWHM
The compressor
VUV FEL
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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)
TOD induced by fiber: 0.5 107 fs3 / TOD by compressor: 1-2 107 fs3
optimization dilemma
bandwidth
transmission
induced TOD
(constant grating
size)
highly dispersive gratings
(1800 lines / mm)


low dispersive gratings
(1200 lines / mm)


the phase shaper - actual design
VUV FEL
HELMHOLTZ GEMEINSCHAFT
folding mirror
Geometry is entirely on-axis. ( design by G. Stobrawa, U. 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)
TEO - imaging
HELMHOLTZ GEMEINSCHAFT
VUV FEL
1:2 imaging
using achromatic lenses
Tilted object → tilted camera
diffraction limited resolution
< 10 µm
for 2 mm field of view
ray tracing well below diffraction limit
wave front propagation
The wedged crystal
(ZnTe)
VUV FEL
HELMHOLTZ GEMEINSCHAFT
Change sensitivity vs. temporal resolution online
0.5mm
10mm
Thick crystal
Thin crystal
Signal
Temporal
resolution




Wedged crystal
HELMHOLTZ GEMEINSCHAFT
VUV FEL
Simulation of EO-Response Function
VUV FEL
HELMHOLTZ GEMEINSCHAFT
First reflection
of THz field
e-beam
Linear diode array
1000 pixel
• incidence angle of laser
• freq. dependent refraction
• freq. dependent EO-coeff.
• group velocity mismatch
• multiple reflection
Simulation of EO-Response Function
VUV FEL
HELMHOLTZ GEMEINSCHAFT
T=-50 fs
origin
17%
100 pixel
5% more charge
20% shorter bunch
Challenge: detection at 1 MHz
VUV FEL
HELMHOLTZ GEMEINSCHAFT
ELIS photo-diode array (silicon video inc.):
 Pixels: 1024 / 8 µm
 Readout: 30 MHz
 1000 pixel -> 30 µs
 128 pixel -> 4 µs
15 ns
Gating 15 ns
Low cost 
ns
Differences between TEO and SPPS
HELMHOLTZ GEMEINSCHAFT
VUV FEL
 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 crystal – change temporal resolution continuously and online
More than 20 motors / 6 cameras – TEO can be entirely remote controlled
EOS
VUV FEL
HELMHOLTZ GEMEINSCHAFT
Timing monitor for the FEL-optical pump-probe Experiments
• Flexible EOS system to test various concepts
•scanning EO
•chirped pulse EO
• Electron
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 …)
EOS - Setup
VUV FEL
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To spectrometer
OTR
TiSa fs pulse
65 nm FWHM / 15 fs
electrons
ZnTe crystal
300 µm
Conclusion
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• 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
VUV FEL
VUV FEL
HELMHOLTZ GEMEINSCHAFT
Dies ist eine
schöne vorlage ...
TEO in numbers
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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:
• 1500 l/mm gratings / 140 mm wide / 1.2m separation
•wavelength transmission: 800 +- 30 nm
•TOD induced = 1.4 107 fs3
fiber:
•170 m long
•Single mode polarization maintaining
•TOD induced = 0.5 107 fs3
• cutoff wavelength < 780 nm
VUV FEL
VUV FEL
HELMHOLTZ GEMEINSCHAFT
Sampling:
• simple analysis
• balanced detector allows high sensitivity
• good synchronization required
• multi-shot method
• arbitrary time window possible
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
Principal of
electro-optical
sampling
PD
Er
camera
Er
Principal of
temporalwavelength
correlation
Space -time correlation method
VUV FEL
HELMHOLTZ GEMEINSCHAFT
laser is „late“
Timing o.k.
laser is „early“
laser
EO-Crystal
Er
v
camera
v
v
the phase shaper - principle
VUV FEL
HELMHOLTZ GEMEINSCHAFT
actual shaper
Time structure and energy budget
VUV FEL
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Ti:Sa oscillator pulses
~ 1600 ns
2.5 nJ Pockels cell 1 MHz
~ 800 ns
9.3 ns
1 MHz
90%
50%
91%
Rotator
0.6%
0.6%
15 pJ
0.6%
stretcher
50%
92%
t = 1600 ns
5%
Pump-probe
experiment
OPA
0.01%
t = 0 ns
108 MHz 98%
10%
90%
X 1000
SHG
10%
PM
SHG
SLM
Feedback
Fiber length
50%
92%
fiber
~ 800 ns
PM
Synchronized to electron beam at EO-crystal
10%
50%
130 pJ
e-bunch
tunnel
2*40 pJ
EO-crystal
gated detector
Synchronized to VUV-FEL beam at sample
Pulse for SHG sampling the fiber length
Pulse for SHG for reference