Streak camera monitoring of the arrival timing jitter

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(No Transcript)
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Streak camera monitoring of the arrival timing
jitter

• Stefan Düsterer
• for the VUV - FEL Team
• E. Plönjes, J. Feldhaus and many others
• MBI- Berlin Lund laser center DCU Dublin
  LURE Paris

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The goal Time-resolved measurements at the FEL
fs-excitation AND fs detection is needed
by BESSY Berlin
VUV-VUV experiments

• Many interesting processes are triggered by
  visible rather than by VUV light
• The visible laser is much more flexible
• larger time-delay (ns ...)
• variable pulse length / chirping
• change color, polarization ...
• Problem jitter between the two independent
  sources

VUV-optical experiments
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Layout of the optical laser system
Wavelength 790 nm ... 830 nm Pulse
duration 100 fs pulse energy
for single laser pulse 50 - 100
µJ Rep rate 1 MHz
Laser parameters
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Layout pump-probe experiments
5 exp. stations
optical laser
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The temporal overlap at the experiment
Overlapping the FEL and the optical pulse
Experimental chamber for the first pump-probe
experiments
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(V)UV streak camera at the experiment
The best so far in UV Zenghu Chang group, Kansas
More about the camera Andrew next talk
streak camera (Berkeley) ( H. Padmore, R.
Falcone, A. MacPhee )
However we need Average over 6000
shots single shot 266 nm 30 nm (266nm)
With courtesy from Howard Padmore
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X-ray streak camera at experiment

• Good idea , however
• Not simple to integrate into experiment (
  intensity, geometry )
• great to find temporal overlap at experiment
• hard to use as online jitter / drift monitor
• User facility
• jitter / drift detection should be independent of
  user experiment

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What am I gonna talk about ?
Using an optical streak camera to monitor the
dipole radiation
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Layout experimental hall
5 exp. stations
optical laser
streak camera
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The problem ...
IR FEL
...100 ms ...
changes from macropulse to macropulse 600 fs
systematic drifts within the macropulse 300 fs
...hours ...
longterm drifts gt ps
the pulses are NOT drawn to scale !
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Strategies for using the optical streak camera
Photoelectrons Reinhard - later

• Jitter close to resolution of streak camera
  (peak detection)
• Reprate too low / space charge problems for
  single shot
• Other methods are better suited for 1 MHz
  detection

EOS - Thursday
systematic drifts within the macropulse 300 fs

• Synchroscan low camera jitter integrate over
  macropulse
• 10 Hz (1D binning) readout works
• rising edge for each macropulse will be
  monitored ( 300 fs)

Macropulse to macropulse 600 fs

• continuous monitoring -gt detection of long term
  drifts
• using as feedback signal for RF shifter in laser

longterm drifts gt ps
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Two photon Above Threshold Ionization (ATI)
M. Meyer, P.OKeeffe LURE
Superposition of visible and VUV pulse in a nobel
gas jet
Electron spectrometer
VUV
Visible fs laser pulse
gas jet
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Single-shot FEL -IR cross correlator

• resolution lt 50 fs
• Parasitic does not destroy
• the FEL pulse

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Single-shot FEL -IR cross correlator
(Proposal by M. Drescher, Universität Bielefeld)
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Strategies for using the optical streak camera

• Jitter close to resolution of streak camera
  (peak detection)
• Reprate too low / space charge problems for
  single shot
• Other methods are better suited for 1 MHz
  detection

systematic drifts within the macropulse 300 fs

• Synchroscan low camera jitter integrate over
  macropulse
• 10 Hz (1D binning) readout works
• rising edge for each macropulse will be
  monitored ( 300 fs)

Macropulse to macropulse 600 fs

• continuous monitoring -gt detection of long term
  drifts
• using as feedback signal for RF shifter in laser

longterm drifts gt ps
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Layout of the dipole radiation beam line
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Location of the dipole experiments
Laser hutch
90 off-axis parabola (4) to focus on slit
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Emission geometry principle limits ?
Collecting mirror
R3.6 m
? the electron bunch shape is accurately mapped
onto the dipole light
Electron trajectory
Path length difference between Different rays
projected to object plane opening angle 3 10
mrad ? 4 fs 20 mrad ? 30 fs
Path length difference between different rays on
the arc lt 3 fs
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Another problem Dispersion
Dipole light is white light
Vacuum window (3mm) Streak camera lens
Bandwidth temporal spread
temporal spread 400 nm 400 fs 12 ps 50
nm 50 fs 1.7 ps 10 nm 10 fs
0.3ps
Ways around ? use band-pass filter (tremendous
loss of photons) ? all reflective optics
(expensive) ? focus directly onto the cathode
(??) ? dont use a streak camera .
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Streak camera test synchroscan, 2ps resolution
Resolution of arrival time jitter expected to be
300 fs
measurements by Ingo Will, MBI Berlin
The delay between two short laserpulses can be
determined with a reproducability of lt100 fs
(FWHM) despite a camera resolution of 2 ps !
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What am I gonna talk about ?
Next topic optical correlation between the
dipole light and the laser
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Optical correlation
Non-linear crystal
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Test experiment - setup

• Timing from 800 nm, 80 fs., 10 Hz repetition
  rate, 2 mJ TiSapphire laser.
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  CCD, PSD
•  
  
  Oscilloscope
•  
• KDP
• 
  ß SHG
• 
  
  Delay stage, ?L
• BS
  Variable Attenuator t
  ?L/ccos(ß/2)
• 
   t0
• Freq. Doubled
• light
  t0t
•  

SHG imagine lens
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Test experiment having 5x107 photons /pulse
1015 photons 5x107 photons ? 106 sum frequency
photons Single shot detection with 1 MHz
readout 30 fs resolution (in demo experiment) in
6 ps window
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Conclusions
Multiple (redundant) jitter diagnostics will be
used (2 EOS, Dipole radiation, Photoelectrons,
x-ray streak) to find out which is best
suited ( XFEL)

• time overlap at the experiments
• Use x-ray streak camera downstream experiment
  (lt1 ps res.)
• Optical streak camera
• Monitor macro pulse to macro pulse jitter ( 300
  fs res.)
• Use as feedback for long term drifts
• Optical correlation FEL and Dipole radiation
• 30 fs resolution
• Detection at 1 MHz

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...
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ps - timing tool
Simple way to get ps overlap just measuring
charge ?
Holzman et al. Appl. Phys Lett. 76, 134 (2000)
2 switches second one grounds the first at ps
delay
Single photoconductive switch