Transcript John T. Costello Photoabsorption Spectroscopy & Imaging Laser-Plasma (Atomic Photoionization with LPP)

Photoabsorption Spectroscopy & Imaging
with Laser-Plasma X-VUV Continua
(Atomic Photoionization with LPP)
John T. Costello
National Centre for Plasma Science & Technology (NCPST)
and School of Physical Sciences, Dublin City University
www.physics.dcu.ie/~jtc & [email protected]
Seminar - Queens University Belfast, March 9th 2004
Outline of Talk
Part I - Laser Plasma 'Line-Free' Continuum Sources

Origin, Brief History & Update
Part II - Dual Laser Plasma Experiments - Some Case Studies

X-VUV Photoabsorption Spectroscopy

VUV (Monochromatic) Photoabsorption Imaging
Part III - Next Steps Atomic Photoionization

Photoionization of Atoms in Intense Laser Fields - ‘Pump
Probe’ Experiments with X-VUV FELs
Collaborators and Contributors
Picosecond Continuum Sources
RAL - Edmund Turcu & Waseem Shaikh
QUB - Ciaran Lewis, Richard O'Rourke and A MacPhee
DCU - Oonagh Meighan and Cormac McGuinness
EUV Absorption Spectroscopy
Rostov - Philipp Dhemekin and Viktor Sukhorukov
DCU - Lar Kiernan, Amit Neogi & Eugene Kennedy
VUV Photoabsorption Imaging Facility - VPIF
Padua -Piergiorgio Nicolosi and Luca Poletto
DCU - John Hirsch, Kevin Kavanagh, Amit Neogi & Eugene Kennedy
DESY ‘Pump Probe’ EU-RTD Project
HasylabJosef Feldhaus, Elke Ploenjes, Kai Tiedke et al.
OrsayMichael Meyer & Patrick O'Keefe,
LundJorgen Larsson et al.
MBIIngo Will et al.
DCUEugene Kennedy & John Hirsch
PaduaP Nicolosi
The DCU - NCPST - CLPR node has 6 labs
focussed on Pulsed Laser Deposition (2) &
Photoabsorption Spectroscopy/ Imaging (4)
Research themes include
Probing matter with fast and ultrafast UV,
extreme-UV and X-ray pulses
(Imaging/Spectroscopy in the UV - Soft X-Ray)
Staff: John T Costello, E T Kennedy, J-P Mosnier & P van Kampen
Post Doctoral Fellows (4):
Deirdre Kilbane
(PVK/JC), 2004 - '2g Photoionization'
Jean-Rene Duclere
(JPM), 2004 - 'Pulsed Laser Deposition'
Incoming-Hugo de Luna (JC), 2004 - 'VUV Imaging/Colliding Plasmas'
Incoming - TBA
(ETK), 2004 - 'ICCD/Plasma Spec./EUV FEL'
Current (CLPR) PhD Students (6-7)
Kevin Kavanangh
(03-JC-'VUV Imaging'),
Adrian Murphy
(03-JC-'SXR PPAS')
Jonathan Mullen
(00-PVK-'Thin Films'),
Ricky O'Haire
(03-JPM- 'PLD'),
Eoin O’Leary
(03-ETK-'VUV LIPS'),
Pat Yeates
(99-ETK-'ICCD/Plasma Diag),
TBA
(incoming 04-PVK/JC- '2g Photoion')
Marie Curie Training Fellows(2):Jaoine Burghexta (Navarra, ETK), Nely
Paravanova (Sofia, JC) & Michael Novotny (CZ, JPM - incoming)
PhDs (03/04)-M Khater(EK), J Hirsch(JC), A McKiernan/M Stapleton(JPM)
Part I Laser Plasma Continua
Laser Plasma Source Parameter Range
Vacuum or
Target
Background Gas
Laser Pulse 1064 nm/
0.01 - 1 J/ 5ps - 10 ns
Plasma
Assisted
Chemistry
Lens
Spot Size = 50 mm (typ.)
F: 1011 - 1014 W.cm-2
Te : 10 - 1000 eV
Ne: 1021 cm-3
Vexpansion  106 cm.s-1
Emitted Atoms,
Ions,
Electrons,
Clusters,
IR - X-ray Radiation
Intense Laser Plasma Interaction
S Elizer, “The Interaction of High Power Lasers with Plasmas”,
IOP Series in Plasma Physics (2002)
Laser Produced ‘Rare Earth’ Continua Physical Origin, History & Update
Laser Plasma Rare Earth XUV Continua
P K Carroll et al., Opt.Lett 2, 72 (1978)
What is the Origin of the Continuum ?
Continua emitted from laser produced
rare-earth (and neighbouring elements)
plasmas are predominantly free-bound in
origin and overlaid by Unresolved Transition Arrays (UTA*) containing many
millions of lines which share the available
oscillator strength.
* J. Bauche, C. Bauche-Arnoult & M. Kalpisch, Phys. Scr 37, 659 (1988)
Brief History/ Highlights of Laser
Plasma Rare-Earth’ Continua -1990
1.
2.
3.
4.
5.
6.
7.
8.
First report of line free continua - P K Carroll et al., Opt.Lett 2, 72 (1978)
First full study/ applications - P K Carroll et al., Appl.Opt. 19, 1454 (1980)
VUV Radiometric Transfer Standard - G O’Sullivan et al., Opt.Lett 7, 31 (1982)
Absolute Calibration with Synchrotron - J Fischer et al, Appl.Opt. 23, 4252 (1984)
Photoelectron Spectroscopy - Ch. Heckenkamp et al., J.Phys.D 14, L203 (1981)
First Study for XUV lithography - D J Nagel et al., Appl.Opt. 19, 1454 (1980)
XUV Reflectometer - S Nakayama et al., Physica Scripta 41, 754 (1990)
First Industrial Application - DuPont - Insulator Band Structure
VUV Reflectance Spectroscopy - R H French, Physica.Scripta 41, 404 (1990) System subsequently made available commercially from ARC
For a review of the early years including applications in
photoabsorption spectroscopy see :
1. J T Costello et al., Physica Scripta T34, 77 (1991)
2. P Nicolosi et al., J.Phys.IV 1, 89 (1991)
Recent Developments in LP Continua I
psec LPLS (RAL/QUB/DCU)
O Meighan et al., Appl.Phys.Lett 70, 1497 (1997)
O Meighan et al., J.Phys.B:AMOP 33, 1159 (2000)
See also, M H Sher et al., Opt.Lett 18, 646 (1993)
Recent Developments in LP Continua -II
MBI Source - 2 trains per second/
25 - 400 Micro-Pulses per train
Laser: 15 mJ - 0.5 mJ per micropulse
& 25 ps pulse duration
XUV Pulse Duration (44 ps - Cu and 73 ps - PET)
11 Ph./1%/sr/train !!
10
M Beck et al., Opt. Comm. 190, pp317-326 (2001)
Recent Developments in LP Continua -III
Photoionization Mass Spectrometry - Osnabruck
R Flesch et al., Rev.Sci.Instrum 71, 1319 (2000)
VUV Photoionization of O2
Laser on
Laser off
Summary - LP Continuum Light Sources
1. Table-top continuum light source now well established
2. Covers Deep-UV to soft X-ray spectral range
3. Pulse duration can be < 100 ps !
4. Continuum flux ~ 1014 photons/pulse/sr/nm (0.8J/10ns)
5. Low cost laboratory source - needs greater awareness
6. Next step Working on (100 ps) + (6ns) Pre-plasma source we already see a flux gain of up to X4 with CuA Murphy et al., Proc SPIE, 4876, 1202 (2003)
Problem of plasma debris for work in clean environments proposals to solve, Michette, O’Sullivan, Attwood,…
Part II - Dual Laser Plasma
Photoabsorption Experiments -
Part II - Section A
Photoabsorption Spectroscopy of Ions
Why do X-VUV ionic photoionization?
Why Photoabsorption ?
 Access to ground/ metastable state (Dark) species
 Electric dipole excitation yields tractable spectra
Why specifically at VUV/XUV photon energies ?
 Photoionization continua
 Inner-shell/ multi-electron excitations
Data relevant to Astrophysical spectra and models
 Laboratory plasma modelling & diagnostics
 Fundamental many-body theory
 X-ray laser schemes
 ICF
Photoionization of Atomic Ions
Not a lot known so far Nice review by John West in:
J.Phys.B:AMOP 34, R45 (2001)
Covers DLP Experiments &
Merged Synchrotron + Ion Beams
Just three sample DLP case studies
Silicon ions - Tsukuba
Carbon ions - Padua
Kr-like ions - Dublin
Dual Laser Plasma
(DLP) Photoabsorption
J T Costello et al., Phys.Scr. T34, 77 (1991),
No tuning required
No vapour required
E T Kennedy et al., Opt.Eng 33, 3984 (1994)
Flexible
Neutral/Multiplycharged/
Refractory Elements
Dx, DT, I(W/cm2)
 Species choice
Backlighter
Isonuclear Sequences
Isoelectronic Sequences
Backlighting Plasma Io
Both Plasmas I = Ioe-snL
Relative Absorption Cross Section
sNL =Ln(Io/I)
DLP Studies on Si - (FOM ) & Tsukuba - I
Motivation - Optical properties of deposited Si nanoparticles
Kouichi Murakami et al.,
Jpn.J.Appl.Phys 35, L735 (1996)
DLP Studies on Si - (FOM ) & Tsukuba - II
Murakami et al.,
Jpn.J.Appl.Phys 33, 2586 (1994)
Pure Si+ spectrum!!
J. T. Costello et al.,
J.Phys.B:AMOP 31, 677 (1998)
Summary - Tsukuba
Work centres on determining conditions under
which clusters .vs. atoms/ atomic ions are
formed with a view to optimising nanocluster
formation and enhancing their optical
properties, (lifetime, efficiency, wavelength, ..)
XUV permits them to access more highly
charged ions in their PLD plumes
The Tsukuba group now combine XUV-DLP
with PLD / Photo-Luminescence Spectroscopy
- potential for 'Closed Loop Control' here
DLP Studies on C Ions (Padua)- I
VUV Photoabsorption - Absolute Cross-sections !
Motivation: Ions of astrophys. interest, tests of databases (Opacity, etc.)
P Recanatini, P Nicolosi & P Villoresi,
Phys. Rev. A 64, Art. No. 012509 (2001)
Spaced resolved emission from a W plasma
in the VUV around (a) 49 nm and (b) 69 nm
Normal Incidence DLP Setup
DLP Studies on Ions (Padua) - II, C+
2.1 mm
3.3 mm
1.2 J on target in line focus: 9 mm X 0.01 mm
Absorption spectra of C+ taken at an inter-plasma delay of 58 ns and at
2.1 and 3.3 mm above the carbon target surface
Summary - Padua
Work centres low-Z ions of astrophysical interest
All isonuclear sequences of Be, B and C measured.
Designed and built DLP systems to work from VUV
to Soft X-ray (Carbon K)
Have determined absolute photoabsorption cross
sections using DLP
Dublin
Have published upwards of 100 papers on DLP
photoabsorption experiments on selected atoms
and ions from all rows of the periodic table.
Motivation - almost always exploration of some
'quirk' of the photoionization process in a many
electron atom !
Kr-like ions -
+
Rb
&
2+
Sr
Why Specifically Kr-like Ions ?
Electronic Configuration
4s24p6
1. Prototypical high-Z closed shell atom - beyond simple Fano theory
2. 30+ years of research in both single and multiphoton ionization
3. Will the photoionization dynamics (q/G) change (a little or a lot ?)
4. How will current many-electron photoionization theory stand up ?
XUV Photoabsorption along an Isoelectronic
(Kr-like) Sequence - I
4s24p6 + hnVUV  4s4p6np + 4s64p4nln’l’  Kr+(4s24p5) + e’l
A Neogi, J T Costello et al., Phys.Rev.A 67, Art. No. 042707 (2003)
NB: Resonance
profile quite
different
XUV Photoabsorption along the Kr
Xsection
Isoelectronic Sequence - II
4s  4p
q-value
14
0.12
12
0.11
3+
Y
10
0.1
0.09
8
0.08
6
0.07
4
0.06
2
0.05
0
0.04
66
68
70
72
74
E (eV)
76
78
80
82
Absorbance
Cross Section (MB)
XUV Photoabsorption along the Kr
Isoelectronic Sequence - III
Kr-like ions - Summary
1. It is clear that the ‘Fano’ profile parameters for the main 4s – np
resonances in each spectrum are very sensitive to degree of ionization.
2. It is also clear that complex doubly excited resonances persist
(at least in the early members of the isoelectronic sequence).
3. Computed cross sections show good agreement with measured spectra.
4. Rescaling the Coulomb interaction is needed to better fit the 4s-5p
resonance in Sr2+
5. We observe that the complex doubly excited resonances straddling the
first 4s-5p resonance in Kr moves to higher photon energy blending with 4s-np
resonances, where n>6.
6. This trend continues to Y3+ where the 4s-5p drops below the 4p threshold
and the 4s-6p becomes almost Lorenztian.
Part II - Section B
VUV Photoabsorption
Imaging
Collaboration between DCU & Univ. Padua
Key paper:
J Hirsch, E Kennedy, J T Costello, L Poletto & P Nicolosi
Rev.Sci. Instrum. 74, 2992 (2003)
VUV Photoabsorption Imaging Principle
John Hirsch et al, J.Appl.Phys. 88, 4953 (2000)
Sample
Io(x,y,l,Dt)
VUV
CCD
I(x,y,l,Dt)
n(l )dl

I  I0e
s
Pass a collimated VUV beam through the plasma sample
and measure the spatial distribution of the absorption.
Motivation
1. Direct imaging of light emitted by a plasma using gated
array detectors (e.g., I-CCD) provides information on
excited species only
2. Probing plasma plumes using tuneable lasers provides
information on non-emitting species but is limited to
wavelengths > 200 nm or so
3. ‘Applied Atomic Photoionization'
Why a pulsed, tuneable and collimated beam ?
• Pulsed
Automatic time resolution:
the VUV pulse duration ~ laser pulse duration (~1-30 ns)
• Tuneable
Can access all resonance lines of all atoms & moderately
charged ions with resonances between 30 nm and 100 nm
(present system)
• Collimated
Can place the sample and CCD anywhere along the beam
Advantages of using a VUV beam
1. VUV light can probe the higher (electron) density regimes not
accessible in visible absorption experiments
2. The refraction of the VUV beam in a plasma is reduced compared
to visible light with deviation angles scaling as l2
3. The images analysis is not complicated by interference patterns
since the VUVcontiuum source has a small coherence length (mms)
4. VUV light can be used to photoionize atoms and ions - this process
simplifies greatly the equation of radiative transfer (no bound states).
5. Fluorescence to electron emission branching ratio for many inner
shell transitions can be 10-4 or even smaller => almost all photons
are converted to electrons
VUV Photoabsorption Imaging Facility-
‘V-P-I-F’
Focussing
Toroidal Mirror
Monochromator
Entrance slit
Exit slit
Grating
Plasma source
Sample Plasma
Collimating
Toroidal Mirror
CCD
VUV Bandpass
Filter
The obligatory picture !!
VUV Monochromator
Mirror Chambers
LPLS Chamber
Sample Plasma
Chamber
VUV-CCD
VPIF Specifications
Time resolution:
~10 ns (200 ps with new EKSPLA)
Inter-plasma delay range:
Delay time jitter:
Monochromator:
VUV photon energy range:
0 - 10 msec
± 1ns
Acton™ VM510 (f/12, f=1.0 m)
10 - 35 eV
VUV bandwidth:
Detector:
0.025 eV @25 eV (50mm/50mm slits)
~0.05 nm @ 50 nm
Andor™ BN-CCD,
Spatial resolution:
1024 x 2048/13 mm x 13 mm pixels
~120 mm (H) x 150 mm (V)
What do we extract from I and Io images ?
Absorbance: A  log 10
Equivalent
Width:
I (x, y,t, l)dl

(
)
 I(x, y,t, l)dl
0
  [I0  I]dl 
WEl  Dl

  I 0 dl 
WEl 
 [1 e
s ( l)NL
]dl
Time resolved Wl maps of Ca plume species
Tune system to 3 unique resonances
Ca:
3p64s2 (1S) - 3p54s23d (1P)
Ca+:
3p64s (2S) - 3p54s23d (2P)
Ca2+:
3p6 (1S) - 3p53d (1P)
Maps of equivalent width of atomic calcium using the 3p-3d resonance
at 39.48 nm (31.4 eV) - 200 mJ on line focus 3mm x 0.015 mm
Maps of equivalent width of Ca+ using the 3p-3d resonance
at 31.4 eV - (200 mJ/15ns on line focus 5 mm x 0.015 mm)
Maps of equivalent width of Ca2+ using the 3p-3d resonance
at 34.7 eV - 200 mJ/15ns on line focus 5mm x 0.015 mm
Expansion of singly ionized calcium plume component using
the 3p-3d resonance at 37.34 nm (33.2 eV)
7 frames: 5 ns, 20 ns, 35 ns, 50 ns, 75 ns, 100 ns &125 ns
PLD Fluence level - 40 mJ/mm2 or 4J/cm2
Q ui ck Ti m e ™ an d a G I F de co m p re ss or ar e n ee de d t o s ee
4 mm
th i s pi c tu r e.
4 mm
Plume COG Position (cm)
Plume Expansion Profile of Singly Charged Ions
Delay (ns)
Ca+ plasma plume velocity
experiment: 1.1 x 106 cms-1
simulation: 9 x 105 cms-1
Ba+ plasma plume velocity
experiment: 5.7 x 105 cms-1
simulation: 5.4 x 105 cms-1
You can also extracts maps of column density,
e.g.,Singly Ionized Barium
Since we measure resonant photoionization, e.g.,
Ba+(5p66s 2S)+h  Ba+*(5p56s6d 2P)  Ba2+ (5p6 1S)+eh = 26.54 eV (46.7 nm) and
the ABSOLUTE VUV photoionization cross-section
for Ba+ has been measured:
Lyon et al., J.Phys.B 19, 4137 (1986)
We should be able to extract maps of column density -
'NL' = ∫n(l)dl
Maps of equivalent width of Ba+ using
the 5p-6d resonance at 26.55 eV (46.7 nm)
Convert from WE to NL
Compute WE for a range of NL and fit a function f(NL) to a plot of NL .vs. WE
Apply pixel by pixel
WE 
 [1 e
s ( l)NL
dl
]dl
Result - Column Density [NL] Maps
(A)
(B)
(C)
(D)
(E)
(F)
100 ns
150 ns
200 ns
300 ns
400 ns
500 ns
VPIF - Summary
VPIF - Provides pulsed, collimated and tuneable VUV
beam for probing dynamic and static samples
Spectral (1000) & spatial (<100 mm) resolution and
divergence (< 0.2 mrad) all in excellent agreement
with ray tracing results
Extracted time and space resolved maps of column density
for various time delays
Measured plume velocity profiles compare quite well
with simple simulations based on adibatic expansion
Current & Future Applications
Space Resolved Thin Film VUV Transmission
and Reflectance Spectroscopy - PVK
‘Colliding-Plasma’ Plume Imaging
Combining ICCD Imaging/Spectroscopy & P/Imag
Non-Resonant Photoionization Imaging
VUV Projection Imaging ?
Photoion Spectroscopy of Ion Beams ?
‘Colliding Stars Model System' 'Colliding Plasmas'
NGC 2346
The shape of this nebula is the result of a violent interaction between two
stars. The image was captured by the Wide Field and Planetary Camera on
the Hubble Space Telescope.
Image Credit: NASA, Massimo Stiavelli, STScI ODButterfly Nebula
First and very preliminary tests
on colliding plasma imaging with
the VPIF
Colliding Plasmas on Flat Target
QuickTime™ and a
GIF decompressor
are needed to see this picture.
Part III - Next steps in fundamental
photoionization studies ?
Atoms and Molecules in Laser Fields
1.
Attosecond pulse generation/ HHG
2.
Photoionization of ‘state prepared’ species
(a) Weak Optical + Weak X-VUV
(b) Intense Optical + Weak (Intense) X-VUV
3.
Atoms, Molecules, Cluster & Ions in Intense Fields
(Multiple-Photon and Optical Field/Tunnel-Ionization)
Free Electron Laser at
Hasylab, DESY, Hamburg
'Laser-like' radiation
in the VUV and EUV
Free electron radiation sources
Josef Feldhaus, DESY, Hamburg
Bending magnet, broad band
 NW x bending magnet
 NU2 x bending
magnet
l1=lu/2g2(1+K2/2)
 NU2 x Ne x bending magnet
NU , NW = # magnetic periods
Ne = # electrons in a bunch
Schematic layout of a SASE FEL
LINAC Tunnel
Experimental Hall
Time table EUV FEL
February 2004:
- complete linac vacuum
- install photon diagnostics in FEL tunnel
Mar.-July 2004:
- injector commissioning
- completion of LINAC
Aug.-Dec. 2004:
- LINAC and FEL commissioning with short
bunch trains
- installation of first two FEL beamlines (~20
µm focus direct beam and high resolution
PGM)
Jan.-March 2005: - commissioning of first FEL beamlines and
gas ionisation monitor
- photon beam diagnostics
Spring 2005:
- first user experiments
X-VUV FELs + Femtosecond OPAsThe Ultimate Photoionization Expt ?
Tuneable:
Ultrafast:
High PRF:
Energy:
Intense:
TTF1: 80 - 110 nm
100 fs pulse duration
1 - 10 bunch trains/sec with up to 11315pulses/bunch
Up to 1 mJ/bunch
100 mJ (single pulse) /100 fs /10 mm => 1015 W.cm-2
•Moving to XUV (TTF2: 2005) and X-ray (2011):
Project Title:‘Pump-Probe’ with DESY-VUV-FEL (EU-RTD)
Aim:
FEL + OPA synchronisation with sub ps jitter
Key Ref:
http://www-hasylab.desy.de/facility/fel/vuv/projects
Partners:
DESY, MBI, DCU, LURE, LLC, BESSY
Femtosecond X-VUV + IR
Pump-Probe Facility,Hasylab, DESY
OPA
Pump-probe experiments in the gas phase
(project: II-02-037-FEL)
M. Meyer et al, LU.R.E., Orsay, France
Participating groups:
HASYLAB, Hamburg, Germany
J. Feldhaus, E. Ploenjes, K. Tiedke
L.U.R.E., Orsay, France
M. Meyer, L. Nahon, P. O'Keeffe
NCPST, Dublin City University, Ireland
J. T. Costello & E. T. Kennedy
Lund Laser Center MAX-Lab, Sweden
J. Larsson, A. L'Huillier, S. Sorenson
Max-Born Institut, Berlin, Germany
I. Will, H. Redlin
Two subsets of experiments
II-A
Direct photoionization in a non-resonant laser field
II-B
Resonant photoionization in a resonant laser field
Let's first look at II-A ‘Direct photoionization'
in a non-resonant laser field*
*Slides provided by Patrick O’Keefe and Michael Meyer, LURE, ORSAY !
Ponderomotive streaking of the ionization potential as a method for measuring pulse
durations in the XUV domain with fs resolution
E.S. Toma, H.G. Muller, P.M. Paul, P. Berger, M. Cheret, P. Agostini, C. LeBlanc, G. Mullot, G. Cheriaux
Phys. Rev. A 62, Art. No. 061801 (2000)
eVUV
IR
presence of IR:
Ar+
3p5
- shift of IP
- broadening of PES peaks
- sidebands
Ar 3p6
Test-experiments at LLC:
M. Meyer, P. O’Keefe (LURE), A. L’Huillier (LLC)
fs-laser system: Ti:Saph. 800 nm, 50 fs, 1 kHz
VUV --> HHG, DT ≈ 30 fs, 1 kHz,
IR --> up to 0.5 mJ --> 1-10 TW/cm2
PES: magnetic bottle spectrometer
- high angular acceptance
- high energy resolution for Ekin < 10 eV
Cross correlation experiments using high order harmonics
H13
H15
H17
H19
H21
H23
50
DT
fs
0
-50
5
10
15
20
Ekin (eV)
e-
E = 15.8 eV
IR
Ar+ 3p5
VUV
Ar 3p6
Generation
(HHG)
l(laser) = 800nm
H11 = 17 eV
H13 = 20 eV
H15 = 23 eV
:
:
But also very interesting are:
Type IIB-Experiments'Resonant photoionization'
in an intense/resonant fields
=>Study intensity controlled autoionization !!
Proposed (approved) experiment at the FEL
Exp.:
Two-photon double-resonant excitation
FEL : hn = 65.1 eV (tunable) Laser : l = 750 - 800 nm (tunable)
Coupling of He Doubly Excited States
2s3d
Intense Laser
2s2p
2s2p 1P – 2s3d 1D
20 fs (34 meV)
VUV
He 1s2
A. I. Magunov, I. Rotter and S. I. Strakhova
J. Phys. B32, 1489 (1999)
H. Bachau, Lambropoulos and Shakeshaft
PRA 34, 4785 (1986)
Bachau, Lambropoulos and Shakeshaft, PRA 34, 4785 (1986)
Laser on Resonance (d2 = 0)
& scan the XUV photon energy
1s2(1S) + hnXUV {2s2p (1P) + (intense)hnLaser <=> 2s3d (1D)}
'Hollow' He
Hollow 'Li'
What about more complex atoms in (intense) laser fields ?
‘Simplest’ complex atom is Li !
'Field Free' Hollow Li
First member of famous MaddenCodling Series - but in He-like Li !
Li+: 1s2(1S) + hnXUV  2s2p (1P)  Li2+(1s) + e’l
Actually first observed in 1977 by
P K Carroll and E T Kennedy, PRL 38, 1068 (1977)
1s22s(2S) + hnXUV  2s22p (2P)  1s2(1S) + el
Satellite to 1st member of the famous
Madden & Codling 2e series in He:
1s2(1S) + (weak) hnXUV-> 2s2p (1P)
“First Observation of a Photon Induced Triply
Excited State in Atomic Lithium”
L Kiernan, J-P Mosnier E T Kennedy, J T Costello
and B F Sonntag, Phys.Rev.Lett 72 2359 (1994)
Laser-Excited Hollow Li
1s22s(2S) + (weak)hnLaser-> 2s22p (2P) + (weak)hnXUV -> 2s2p2 (2D)
Experiment - D Cubannes et al. PRL 77, 2194, (1996)
Hollow Li in an intense laser field
1s22s(2S) + hnXUV-> {2s22p (2P) + (intense)hnLaser <-> 2s23d (2D)}
Theory- L Madsen, P Schlagheck and P Lambropoulos, PRL 85, 42 (2000)
Photoionization of Atoms
in Intense Fields - Predictions
L Madsen, P Schlagheck and P Lambropoulos, PRL Vol 85, pp42-45 (2000)
Laser on Resonance
Scan XUV Energy
XUV field on resonance
Scan laser frequency
Could this be done with a
laser plasma X-VUV source
and a table top OPA ?
In principle YES
You just cross the sample with intense
laser (OPA) and weak XUV beams
Need wavelength selection and high (average)
X-VUV intensity
Count rate low ~ 1 ion/laser shot for He with Volint ~ 10 -3 cm-3
But - the Ca+ 3p-subshell resonances have:
1. Cross sections up to 2500 MB .vs. < 0.1MB for Li
2. Excitation widths up to 100 meV
3. A VUV (normal incidence) excitation energy (31 eV)
SigRaw (MB)
+
Ca . ALS Measurem ent. 5 meV per point.
2500
SigRaw (MB)
2000
1500
1000
500
0
28
29
30
31
32
Photon Energy (eV)
33
34
Scheme- Ca+:
3p64s (2S) + hnXUV-> {3p53d4s (2P) + hnLaser <=> 3p53d4p (2D)}
(33.2 eV)
or
3p64s (2S) + hnXUV-> {3p54s2 (2P) + hnLaser <=> 3p54s4p (2D)}
(28.2 and 28.5 eV)
Exploratory study in DCU - Summer 2004
Photoionization Summary
Single VUV - X-ray photon photoionization (and concomitant
correlation) in atoms and ions is now well understood
Photoionization of atoms (much less so ions) in intense IR/VIS
laser fields is now well established also (MPI .vs. Tunnelling)
What’s left ? - Cross-over of the above two ?
Atoms in intense VUV/XUV (high frequency) fields first result - Nature 2002
Resonant/ non-resonant photoionization of atoms in intense
resonant/non-resonant laser fields
Why bother ? (Where are the applications)
Pushing limits - exploring new spaces - new science & technol.