EO systems at the DESY VUV-FEL

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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)

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The 2 EOS systems
Experiments
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TimingEO
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

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Layout pump-probe experiments
optical laser
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TEO
Pockels cell
50 beam splitter
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The laser hutch
overview picture - CDR layout
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The TEO layout - in the laser hutch
laser hutch - CDR layout
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The TEO layout - in the tunnel
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TEO - first steps...
Laser hutch
Accelerator tunnel
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TEO - simulations
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
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introducing LAB II simulation software

• 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

Free download at www.lab2.de
Based on LabView
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Lab II - simulation of TEO
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The 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)
TOD induced by fiber 0.5 107 fs3 / TOD by
compressor 1-2 107 fs3
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the phase shaper - actual design
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)

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TEO - imaging
12 imaging using achromatic lenses Tilted
object ? tilted camera diffraction limited
resolution lt 10 µm for 2 mm field of view
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The wedged crystal (ZnTe)
Change sensitivity vs. temporal resolution online
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Wedged crystal
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Simulation of EO-Response Function

• incidence angle of laser
• freq. dependent refraction
• freq. dependent EO-coeff.
• group velocity mismatch
• multiple reflection

First reflection of THz field
e-beam
Linear diode array 1000 pixel
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Simulation of EO-Response Function
T-50 fs
origin
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100 pixel
5 more charge
20 shorter bunch
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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 -gt 30 µs
• 128 pixel -gt 4 µs
• Gating 15 ns
• Low cost ?

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Differences 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 crystal change temporal resolution
  continuously and online
• More than 20 motors / 6 cameras TEO can be
  entirely remote controlled

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EOS
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 -gt EOS in container ( test of
  crystals )

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EOS - Setup
To spectrometer
OTR
TiSa fs pulse 65 nm FWHM / 15 fs
electrons
ZnTe crystal 300 µm
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Conclusion

• 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

• schöne vorlage ...

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TEO in numbers

• 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 lt 780 nm

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Space -time correlation method
Timing o.k.
laser
EO-Crystal
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the phase shaper - principle
actual shaper
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Time structure and energy budget
TiSa oscillator pulses
1600 ns
Pockels cell 1 MHz
2.5 nJ
1 MHz
X 1000
Pump-probe experiment
90
OPA
0.01
9.3 ns
800 ns
108 MHz
?t 0 ns
98
10
10
SHG
92
91
90
Rotator
0.6
50
0.6
?t 1600 ns
5
0.6
PM
stretcher
15 pJ
SHG
SLM
Feedback Fiber length
PM
fiber
92
800 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
10
tunnel
50
130 pJ
e-bunch
240 pJ
EO-crystal
gated detector