The European
X-Ray Laser Project
Report on the FEL optics activities
Damage iinvestigations
D
ti ti
of FEL relevant optics
Hubertus Wabnitz and Kai Tiedtke
H. Wabnitz/ K. Tiedtke, 29. 01.2008
XFEL
The European
X-Ray Laser Project
XFEL
Outline
Motivation
Measurement technique
and experimental set-up
Former experimental results and modelling
Experimental campaign in November
Conclusion
H. Wabnitz/ K. Tiedtke, 29. 01.2008
The European
X-Ray Laser Project
XFEL
Definition of damage
What can be regarded as damage?
Irreversible
- Single shot damage: Ablation …
- Multishot damage: non
non-thermal
thermal
near threshold damage, ageing…
thermal
fatigue
Reversible
- Multishot damage: Thermal degradation of optics
no dissipation in between bunchtrains
H. Wabnitz/ K. Tiedtke, 29. 01.2008
46nm amorphous C
on Silicon
at ~1012 W/cm2
The European
X-Ray Laser Project
XFEL
Why are we suspicious at all?
Trivial but true:
There is no experience with XFEL light sources yet
and there is a tremendous difference to synchrotrons!!
Parameter
Unit
SASE 1
Photon energy
keV
12.4
12.4
3.1
3.1
0.8
0.25
1012
1012
1.6 × 1013
1.6 × 1013
1.0× 1014
3.7 × 1014
Photons/pulse
SASE 2
SASE 3
P l energy
Pulse
mJ
J
2
2
8
8
13
15
Pulse duration
fs
100
100
100
100
100
100
Photon beam
divergence
g
µrad
1
0.84
3.4
3.4
11.4
18
Distance
Undulator – Exp.hall
m
960
900
400
400
400
400
~ Beam diameter
(FWHM) at exp
exp. hall
mm
0.96
0.76
3.1
1.4
4.6
7.2
W/cm²
2.7 × 1012
4.4 × 1012
1.1 × 1012
5.5 × 1012
8.0 × 1011
3.6 × 1011
~ Intensity
(unfocused)
F comparison:
For
i
At Doris
D i ~ 106 W/cm
W/ 2 maximum
i
H. Wabnitz/ K. Tiedtke, 29. 01.2008
The European
X-Ray Laser Project
XFEL
Why are we suspicious at all?
Trivial but true:
There is no experience with XFEL light sources yet
and there is a tremendous difference to synchrotrons!!
Parameter
Unit
SASE 1
Photon energy
keV
12.4
12.4
3.1
3.1
0.8
0.25
1012
1012
1.6 × 1013
1.6 × 1013
1.0× 1014
3.7 × 1014
Photons/pulse
SASE 2
SASE 3
P l energy
Pulse
mJ
J
2
2
8
8
13
15
Pulse duration
fs
100
100
100
100
100
100
Photon beam
divergence
g
µrad
1
0.84
3.4
3.4
11.4
18
Distance
Undulator – Exp.hall
m
960
900
400
400
400
400
~ Beam diameter
(FWHM) at exp
exp. hall
mm
0.96
0.76
3.1
1.4
4.6
7.2
~ Intensity
(unfocused)
2.7 ×
4.4 ×
1.1 ×
5.5 ×
8.0 ×
1012
1012
1012
1012
1011
F comparison:
For
i
At Doris
D i ~ 106 W/cm
W/ 2 maximum
i
per pulse
l
W/cm²
H. Wabnitz/ K. Tiedtke, 29. 01.2008
3.6 ×
1011
The European
X-Ray Laser Project
XFEL
Why do we need mirrors?
Safety reasons:
beam off-set hinders Bremstrahlung etc. to enter experimental area
Photon beam distribution to different end stations
H. Wabnitz/ K. Tiedtke, 29. 01.2008
The European
X-Ray Laser Project
XFEL
How to protect the mirrors?
Long distance
Æ let photon beam diverge
distance to undulator
Gracing incidence angles
Æ stretched footprint
photon beam
Mirror
α
Footprint
p
length
g ~1/sinα
10
100
1000
0 01
0,01
(mrad)
at 2 mrad
elongation of ~500
Æ footprint‘s length
~0.7m (6σ at 12.4 keV)
100
10
01
0,1
1
10
100
1,00
Reflectivity
Footprint mag
gnification
1000
1
C at 12.4 keV
0,75
0,50
0,25
1
0,1
1
10
100
Incidence angle (deg)
H. Wabnitz/ K. Tiedtke, 29. 01.2008
0,00
1E-4
1E-3
0,01
0,1
Incidence angle (rad)
1
The European
X-Ray Laser Project
XFEL
Atomic dose model
DA = E pulse (1 − R ) / Aproj latt n A
Æ low Z elements favour low dose
Æ dose
d
off C coated
t d mirrors
i
always below 10meV/atom
ÆSASE 3 most critical
(higher fluence
fluence=14mJ,
14mJ, α
α=10
10 mrad)
Reflectiv
vity
Att. length (m))
A
Implications
0 75
0,75
C
Si
Au (4mrad)
Au
0,50
0,25
1E-5
1E-7
10
0
10
-1
10
-2
10
-3
10
-4
10
-5
0
5000
10000
15000
20000
Photon energy
gy ((eV))
H. Wabnitz/ K. Tiedtke, 29. 01.2008
α=2mrad
1,00
Dose ((eV/atom)
Epulse : Energy per pulse
R
: Reflectivity
Aproj : p
proj.
j beam footprint
p
area
latt : 1/e attenuation length
nA : density of atoms
SASE 1 and SASE 2
Double-mirror
25000
30000
The European
X-Ray Laser Project
XFEL
Benefits
Enables reliable extrapolation to high photon energies
Æ beam line optics can be ordered
Possibly higher deflection angles Æ might relax constraints on beamline optics
for upgrade (FLASH2, sFLASH)
Investigation of multi-layers
Æ new optical schemes
H. Wabnitz/ K. Tiedtke, 29. 01.2008
The European
X-Ray Laser Project
XFEL
Experimental setup (very principal sketch)
UHV exp. chamber
Attenuator
adjust pulse
energy level
GMD
measure
pulse energy
Fast
shutter
pick single
pulses
Sample
holder
Ellip. mirror
Light
Microscope
(few micron resolution)
movement relative to the focus
H. Wabnitz/ K. Tiedtke, 29. 01.2008
The European
X-Ray Laser Project
XFEL
Examination methods
Light microscope for fast
but rough examination.
32nm
21.7nm
Post mortem examination
Æ AFM ((morphology)
p
gy)
Æ Nomarsky (optical properties)
Æ Micro Raman (graphitisation...)
13.5nm
AFM pictures of PMMA for various wavelengths
H. Wabnitz/ K. Tiedtke, 29. 01.2008
7.1nm
The European
X-Ray Laser Project
Damage threshold
One physical explanation is the onset of melting
H. Wabnitz/ K. Tiedtke, 29. 01.2008
XFEL
The European
X-Ray Laser Project
XFEL
Pl
Planned
d investigations
i
ti ti
for
f recentt campaign
i
Extrapolation to shorter wavelengths
Grazing incidence measurements
Example:Carbon
Example:Carbon
Example: Silicon
… and of course for a bunch of other materials
H. Wabnitz/ K. Tiedtke, 29. 01.2008
The European
X-Ray Laser Project
Recent beamtime
H. Wabnitz/ K. Tiedtke, 29. 01.2008
XFEL
The European
X-Ray Laser Project
XFEL
Beamline alignment
1st shift : 8h @7nm
2nd shift: 12h @13.5nm
3rd shift:
„
4th shift:
„
5th shift:
„
Æ found unexpected imprints
Æ beam characterisation, verified misalignment of beamline
Æ „ A very special FEL mode“
Æ further beamline alignment
alignment, beam characterisation
Æ first data under reasonable conditions, but…
Focal imprint in PMMA:
1st shift at 13.5nm
– misaligned beamline -
H. Wabnitz/ K. Tiedtke, 29. 01.2008
Focal imprint in PMMA:
3rd shift at 13.5nm
improved alignment
The European
X-Ray Laser Project
XFEL
Beam shape
Image of photon beam
vertical feature is a bug
( diffraction at edge, somewhere)
λ=13.5nm, 3mm-aperture
beam attenuated
with a 5µm thick Silicon foil
protect CCD chip
p
to p
concentric feature expected
( diffraction at beam aperture)
H. Wabnitz/ K. Tiedtke, 29. 01.2008
The European
X-Ray Laser Project
XFEL
Analysis
Multilayer samples
Got reasonable results (dam
(dam. thresholds
thresholds…))
with „4 spot“ assumption
Æ fulfilled only for stable beam conditions!!
1<2
1>2
1>>2
„Flipping
Fli i iintensities“
t
iti “
Æ unstable beam conditions
1
2
1
2
H. Wabnitz/ K. Tiedtke, 29. 01.2008
1
2
The European
X-Ray Laser Project
XFEL
Conclusions
Successful:
- Data taking scheme and „shot to shot“ correlation
- Major input to beamline commissioning
- Estimation of damage thresholds for few materials
Painful:
- Spent 80% of beamtime for comissioning
- Largest part of measurement programme not accomplished
Thoughtful:
- For quantitative measurements
the commissioning time might be not appropriate
H. Wabnitz/ K. Tiedtke, 29. 01.2008
The European
X-Ray Laser Project
XFEL
With contributions from
Collaborations
- Mirror coatings
Thin Film Technology GKSS-Geesthacht
- Experimental set-up
Institute of Physics, Warsaw
FEL facilities:
- Daresbury Laboratory,Warrington
- Sincrotrone Trieste,
Trieste,Triest
,Triest
- SPring
SPring--8,Hyogo
- LCLS
- Sample investigation (AFM…)
Institute of Physics/ASCR, Prague
- Metrology lab
BESSY,Berlin
- Multilayers
FOM-Institute for Plasma Physics, Rijnhuizen
- Mirror Manufacture
Zeiss
- Analysis and Modelling
Lawrence Livermore Lab
H. Wabnitz/ K. Tiedtke, 29. 01.2008
Also participation in experimental campaign:
Sven Toleikis
The European
X-Ray Laser Project
Last but not least
And
many thanks to you
for operating the machine
H. Wabnitz/ K. Tiedtke, 29. 01.2008
XFEL
The European
X-Ray Laser Project
The end
H. Wabnitz/ K. Tiedtke, 29. 01.2008
XFEL