Transcript VUV FEL HELMHOLTZ GEMEINSCHAFT

HELMHOLTZ GEMEINSCHAFT
VUV FEL
VUV FEL
HELMHOLTZ GEMEINSCHAFT
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
The goal: Time-resolved measurements at the FEL
VUV FEL
HELMHOLTZ GEMEINSCHAFT
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
VUV-optical experiments
 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
Layout of the optical laser system
VUV FEL
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Laser parameters
Wavelength:
Pulse duration:
pulse energy for single laser pulse:
Rep rate
790 nm ... 830 nm
~100 fs
50 - 100 µJ
1 MHz
Layout: pump-probe experiments
VUV FEL
HELMHOLTZ GEMEINSCHAFT
5 exp. stations
FEL pulse
Optical pulse
optical
laser
The temporal overlap at the experiment
VUV FEL
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Overlapping the FEL
Experimental chamber for the first pump-probe experiments
and the optical pulse
X-ray streak camera
(V)UV streak camera at the experiment
VUV FEL
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The best so far in UV:
Zenghu Chang group, Kansas
0.66ps
Intensity
50
380fs
400fs
streak camera (Berkeley)
( H. Padmore, R. Falcone, A. MacPhee …)
0
0
2
4
time(ps)
However:
Average over 6000 shots
266 nm
More about the
camera
we need:
Andrew
– next talk
single shot
30 nm (+266nm)
With courtesy from
Howard Padmore
X-ray streak camera at experiment
HELMHOLTZ GEMEINSCHAFT
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
VUV FEL
What am I gonna talk about ?
VUV FEL
HELMHOLTZ GEMEINSCHAFT
Using an optical streak camera
to monitor the dipole radiation
Layout: experimental hall
VUV FEL
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5 exp. stations
FEL pulse
Optical pulse
VUV pulse
Electrons
optical
laser
streak camera
Dipole radiation
Dipole radiation
The problem ...
VUV FEL
HELMHOLTZ GEMEINSCHAFT
IR
...100 ms ...
FEL
systematic drifts within
changes from macropulse
the macropulse
to macropulse
~300 fs
~ 600 fs
...hours ...
longterm drifts
> ps
the pulses are NOT drawn to scale !
Strategies for using the optical streak camera
HELMHOLTZ GEMEINSCHAFT
Photoelectron
s
VUV FEL
 Jitter close to resolution of streak camera (peak detection)
systematic drifts within the macropulse
~300 fs
Reinhard
- shot
 Reprate too low / space charge problems
for single
EOS Thursday
later
 Other methods are better suited for 1 MHz
detection
 Synchroscan – low camera jitter – integrate over macropulse
Macropulse to macropulse
~ 600 fs
 10 Hz (1D binning) readout works
 rising edge for each macropulse will be monitored ( ~300 fs)
 continuous monitoring -> detection of long term drifts
longterm drifts
> ps
 using as feedback signal for RF shifter in laser
Two photon Above Threshold Ionization (ATI)
M. Meyer,
P.O´Keeffe
LURE
VUV FEL
HELMHOLTZ GEMEINSCHAFT
Superposition of visible and VUV
pulse in a nobel gas jet
Electron
spectrometer
VUV
Visible
fs laser pulse
gas jet
Single-shot FEL -IR cross correlator
VUV FEL
HELMHOLTZ GEMEINSCHAFT
visible strong fs- laser pulse
Gas jet
FEL SASE pulse
• resolution < 50 fs
• Parasitic – does not destroy
the FEL pulse
Electron energy
Photo electrons
(1D) imaging
electron spectrometer
spatial coordinate
Single-shot FEL -IR cross correlator
VUV FEL
HELMHOLTZ GEMEINSCHAFT
(Proposal by M. Drescher, Universität Bielefeld)
Strategies for using the optical streak camera
VUV FEL
HELMHOLTZ GEMEINSCHAFT
 Jitter close to resolution of streak camera (peak detection)
systematic drifts within the macropulse
~300 fs
 Reprate too low / space charge problems for single shot
 Other methods are better suited for 1 MHz detection
 Synchroscan – low camera jitter – integrate over macropulse
Macropulse to macropulse
~ 600 fs
 10 Hz (1D binning) readout works
 rising edge for each macropulse will be monitored ( ~300 fs)
 continuous monitoring -> detection of long term drifts
longterm drifts
> ps
 using as feedback signal for RF shifter in laser
Layout of the dipole radiation beam line
VUV FEL
HELMHOLTZ GEMEINSCHAFT
electrons
Spherical collection mirror
2” diameter – 2.3 m focal length
→ 20 mrad acceptance
~ 5 107 visible photons
Location of the “dipole experiments”
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Laser hutch
90° off-axis parabola (4”)
to focus on slit
40 µm spot size
- ZEMAX simulation-
Emission geometry – principle limits ?
VUV FEL
HELMHOLTZ GEMEINSCHAFT
Collecting mirror
R=3.6 m
→ the electron bunch shape
is accurately mapped
onto the dipole light
Electron
trajectory Rays projected to object plane
Path length difference between
Path length difference between
different rays on the arc
< 3 fs
Different rays
projected to object plane
~ opening angle 3
10 mrad → 4 fs
20 mrad → 30 fs
Another problem: Dispersion
VUV FEL
HELMHOLTZ GEMEINSCHAFT
Dipole light is white light
Vacuum window (3mm)
Streak camera lens
temporal spread
temporal spread
Bandwidth:
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 (??)
● don’t use a streak camera ….
Measurements :
TTF Phase I by Ch. Gerth
Streak camera test – synchroscan, 2ps resolution
VUV FEL
HELMHOLTZ GEMEINSCHAFT
Resolution of arrival time jitter
expected to be 300 fs
33 ps
blue lines:
measured data
33 ps
time
33 ps
read lines:
fitted data
(sum of two
Gaussian pulses)
delay:
delay = 0.034 ps
delay = 0.035 ps
delay = 0.035 ps
measurements by Ingo Will, MBI Berlin
The delay between two short laserpulses
can be determined with a reproducability
of <100 fs (FWHM) – despite a camera
resolution of 2 ps !
standard deviation
of the measured
delay in a series
of 20 shots
What am I gonna talk about ?
VUV FEL
HELMHOLTZ GEMEINSCHAFT
Next topic
optical correlation between
the dipole light and the laser
Optical correlation
VUV FEL
HELMHOLTZ GEMEINSCHAFT
fs-laser
Non-linear
crystal
Dipole radiation
Line focus
Test experiment - setup
VUV FEL
HELMHOLTZ GEMEINSCHAFT
Timing from 800 nm, 80 fs., 10 Hz repetition rate, ~2 mJ Ti:Sapphire laser.
CCD, PSD
Oscilloscope
SHG imagine
lens
KDP
β
SHG
Delay stage, ΔL
BS
Freq. Doubled
light
Variable Attenuator
t0
t0+τ
τ = ΔL/ccos(β/2)
Test experiment
having 5x107 photons /pulse
VUV FEL
HELMHOLTZ GEMEINSCHAFT
8
6
Delay stage position ~0.79 mm
Delay stage position ~0.78 mm
4
3
2
1
SFM intensity, arb. unit
Intensity, (arb.units)
5
1.5
1.0
0.5
Delay stage displacement
0
0.0
10.0 -30011.4
-250
~340 fsec
2.0
Relative SFM intensity, arb. unit
SFM Intensity
Background
Delay stage position ~0.80 mm
2.0
Delay stage displacement, mm
7
1.5
1.0
0.5
0.0
12.9 -150 14.3
-200
-100
15.7 0
-50
CCD array
readout,
mm
Time
shift, fs
17.1
50
18.6150
100
20.0
200
-3.1
-2.0
-1.0
0.0
1.0
2.0
Time shift between independent light pulses, ps
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
3.1
Conclusions
VUV FEL
HELMHOLTZ GEMEINSCHAFT
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 (<1 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
VUV FEL
HELMHOLTZ GEMEINSCHAFT
...
ps - timing tool
VUV FEL
HELMHOLTZ GEMEINSCHAFT
Simple way to get ps overlap – just measuring charge ?
Holzman et al. Appl. Phys Lett. 76, 134 (2000)
Single photoconductive switch
2 switches
second one grounds the first at ps delay