Photoionization of Atoms
with the ‘FLASH’ XUV FEL
A (very) Short Progress Report
John T. Costello
National Centre for Plasma Science & Technology (NCPST)/
School of Physical Sciences, Dublin City University
www.physics.dcu.ie/~jtc
Yangtze University, 26th October 2006
Outline of the Talk
1. Introduction (Who are we ?, What do we do ?)
2. Orientation (Ultrafast and FELs)
3. Synchronising a femtosecond laser to a FEL
4. Summary
By the way: XUV = eXtreme UltraViolet
Who are we ?
Laser-Plasma/Atomic Physics Group of the NCPST
Academic Staff (4): John T. Costello, Eugene T. Kennedy (now VPR),
Jean-Paul Mosnier and Paul van Kampen
Funded by:
SFI - Frontiers and Investigator
Post Doctoral Fesearchers (6):
Dr. Kevin Kavanangh (JC)
HEA - PRTLI and North-South
Dr. Hugo de Luna (JC)
IRCSET - Embark & BRGS
Dr. Jofre Pedrogosa (JC)
Enterprise Ireland - BRGS
Dr. Brendan Doggett (JPM)
EU - Marie Curie
Dr. Subhananda Chakrabarti (JPM)
Dr. Pat Yeates (ETK)
Current PhD students (8):
Caroline Banahan, John Dardis, Padraig Hough
Rick O'Hare, Conor McLoughlin, Eoin O’Leary
Dave Smith, Tommy Walsh
Visiting PhD students: Alice Deliseryes (Belfast) (usually 2 per year)
What do we do ?
DCU
Pico/Nanosecond Laser Plasma Light Sources
VUV, XUV & X-ray Photoabsorption Spectroscopy
Emission & Photoabsorption Imaging
VUV LIPS for Analytical Purposes
ICCD Imaging and Spectroscopy of PLD Plumes
Aarhus/Berkeley (ALS) Synchrotrons
Photoion and Photoelectron Spectroscopy
Hamburg - FEL
Femtosecond IR+XUV Facility Development
Orientation - Timescales in Physics
ULTRAFAST - HOW FAST IS FAST ?
Timescales in Physics
One
Computer Camera
Human existence
month
Age
of
clock cycle flash
pyramids
10 fs light pulse
Age of universe
1 minute
-14
10
-9
10
-4
10
1
10
6
10
11
10
16
10
Time (seconds)
zs
10-21 s
as
10-18 s
fs
10-15 s
ps
10-12 s
SCALES - ORIENTATION
The Metric System - Prefixes
Big
Small
Milli (m)
Micro (µ)
Nano (n)
Pico (p)
Femto (f)
Atto (a)
Zepto (z)
10-3
10-6
10-9
10-12
10-15
10-18
10-21
Kilo (k)
Mega (M)
Giga (G)
Tera (T)
Peta (P)
Exa (E)
Zetta (Z)
103
106
109
1012
1015
1018
1021
Shortest Pulse Duration (fs)
Ultrafast Lasers mid.1980s - late 1990s
Active mode locking
1000
Passive mode locking
100
Colliding pulse
mode locking
10
Extra-cavity pulse
compression
A 4.5-fs pulse…
'65
'70
'75
'80
'85
Year
'90
Current record:
4.0 fsec Baltuska et al.
OPT LETT Vol 27,
pp 306-308, 2002
'95
Deeper - Free Electron Laser at
Hasylab, DESY, Hamburg
'Laser-like' radiation in the Extreme-UV
(E=hc/λ, Wavelength ~13 - 50 nm)
Eventually EU will have an X-FEL !!
‘FLASH’Free electron LASer in Hamburg
Hasylab FEL
Tunnel &
Experimental Hall
SASE-FEL Operating Principle
SASE: http://flash.desy.de
Electrons from the LINAC electrons propagate through the undulator, a
periodic arrangement of magnets forces the electrons to follow a
slalom course. In the process, each individual electron radiates a bright
and collimated XUV pulse of radiation. Because these flashes are faster
than the electrons speeding along their zigzag path, they overtake the
electrons flying ahead of them. At the same time, they interact with
the electrons they pass along the way, accelerating some of them and
slowing others down. As a result, the electrons gradually organize
themselves into a multitude of thin disks. By the time the electrons
reach the end of the undulator, this layered structure is fully formed.
The key property of the structure is the fact that all of the electrons
in a given layer emit their light “in sync.” This produces extremely short
and intense X-ray flashes with the properties of laser light.This is the
SASE principle of self-amplified spontaneous emission. The key feature
here is that the wavelength can be selected according to the users’
specific needs, unlike existing XUV lasers. The electron acceleration only
needs to be adjusted to achieve the desired wavelength. The mirrors
normally required to amplify laser light are not needed at all for this
process – nor are laser mirrors available in any case for wavelengths
< 100 nanometers.
FLASH SPECIFICATIONS
Wavelength:
6 - 60nm (eXtreme-UV)!
Pulse Energy(E): 50 - 150 µJ
Pulse length(τ):
< 30 fs
Spot Size (D):
< 50 µm
Irradiance [(E/D2.τ)]:>1013 W.cm-2
Up to 800 pulses per train at 10 trains per second !!
Two-Colour ‘FLASH’ Collaboration
LIXAM (Orsay, France)
D. Cubaynes, P. O’Keeffe, M. Meyer
DESY (Hamburg, Germany)
S. Düsterer, P. Radcliffe, H. Redlin, J. Feldhaus
Dublin City University (Ireland)
J. Dardis, K. Kavanagh, E. Kennedy, H. Luna,
J. Pedregosa-Gutierrez, P. Yeates, J. T. Costello
Queens University Belfast (N. Ireland, UK)
A. Delserieys, Ph. Orr, D. Riley, C. Lewis
Thanks to AG Photon (R Treusch et al.) & AG Machine (M Yurkov et al.)
DESY VUV-FEL Experimental Hall - BL 2
(August 22 - September 4, 2005)
Photoelectric effect for atoms
-) = hυ - IP
+
KE
(e
A + hυ = A + e
- photodiode
- thermopile
Experimental setup
MBES: Magnetic Bottle
Electron Spectrometer
4π collection angle
razor blade
TOF : 65 cm
phosphor screen
e-
MCP
µ - metal
solenoid
T = 6 x 10-4 T
grids
- U(ret)
permanent
magnet
T= 0.5 T
FEL
One-photon ionization of Xe
Xe (5p6) + hνFEL → Xe (5p5 2P1/2,3/2) + εl
S. Düsterer, J T Costello, E T Kennedy et al., Opt. Lett 31, 1750 (2006)
intensity (V)
Xenon
U(ret) = -15V
P(Xe) = 1 x 10-6 mbar
hν (FEL) = 38.5 eV
70 mV
5p
105
-
106
electrons
I (FEL) = 3 - 5 µJ
→ 8 x 1011 photons/pulse
time-of-flight (ns)
II - Synchronising the FEL and Optical
Laser on a Femtosecond Timescale
bending magnet
LINAC
e-
UNDULATOR -FEL
6 - 60 nm,
30 fs, 50 - 150 µJ
electrons
FEL to user
visible
synchrotron
radiation
Ti:Sa laser : 790 nm – 830 nm
150 fs , 10 - 30 µJ
Nd:YLF pump laser : 523 nm
12 ps , 200-300 µJ
TTF clock
from injector rack
- 300 m long cables
Fs OPA built by Max-Born-Institut, Berlin
I. Will, H. Redlin
opt. laser to user
synchroscan streak
camera - slow
feedback
goal: drift < ps / h
II - Synchronising the FEL and Optical
Laser on a Femtosecond Timescale
"Photoionization of atoms
in intense optical laser fields"
Electron
Spectrometer
VUV
Visible
fs laser pulse
Optical Oscilloscope
with < 10 fsec
resolution
2-Colour Photoelectron Spectroscopy
M. Meyer, E. T. Kennedy, J. T. Costello et al.Phys. Rev. A 74,
Rapid Communication Art. No. 011401 (2006)
Two colour above threshold
ionization (ATI)
Superposition of visible and
VUV pulses in a gas jet
J. M. Schins et al., Phys. Rev. Lett. 73, 2180 (1994).
E.S. Toma et al. Phys. Rev. A 62, 061801 (2000)
Electron
Spectrometer
hwir =1.55eV
VUV
Visible
fs laser pulse
gas jet
Sideband
intensity very
Sensitive to
overlap
Ar(IP)
15.76 eV
M. Meyer,
P.O´Keeffe
Xe Sidebands - 25.5 nm + 800 nm
Femtosecond FEL-Laser
Cross Correlation
Measurement
Using He
Sideband
FEL: 25.5 nm, 10 µJ,
>50µm focus,
50 fs > 1012 Wcm2
Laser : 800 nm, 25 µJ,
<50 µm Focus,
100 fs, > 1012 Wcm2
M. Meyer, E. T. Kennedy, J. T. Costello et al.,
Submitted to Applied Physics Letters (2006)
Jitter below
1 ps - design
Goal of EU-RTD
project
Outlook
1. So now we have a technique to measure the time delay
between and XUV/X-ray (ionising) laser pulse and and optical
laser pulse on a femtosecond timescale - ultrafast
oscilloscope
2. The collaboration is producing valuable data for the machine
guys to really model/understand the dynamics of XUV FELs
3. Still lots of open questions on intense XUV + intense IR
interactions with atoms (and ions) which we are now
addressing - see Physical Review and Applied Physics
Letters in 2006 and 2007 for more news on our work.
The future - attosecond framing camera:
Seeing the electric field of a fs pulse !
Ference Krausz et al.
MPI, Garching, Germany
Outlook for the future
Thank you for your attention and I
wish you well in your physics studies
Remember !!
Still lots of open questions on intense XUV +
intense optical laser interactions with atoms
(and ions) which we are now addressing - see
Physical Review and Applied Physics Letters in
2006 and 2007 for more news on our work and
how we are progressing.