Photoabsorption Spectroscopy & Imaging with
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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 & [email protected] .ie.

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John t costello

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 & [email protected]

Interchannel interaction in photoionization of atoms and photodissociation of molecules, Riezlern, Austria July 12, 2005

John t costello

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

John t costello

Collaborators and Contributors

Picosecond X-VUV Continuum Sources

RAL - E Turcu & W Shaikh

QUB - C Lewis, R O'Rourke and A MacPhee

DCU - O Meighan and C McGuinness

EUV Absorption Spectroscopy

Rostov - P Demekhin, B Lagutin and V Sukhorukov

DCU - P Yeates, A Neogi, C Banahan, D Kilbane, P van Kampen and

E Kennedy

VUV Photoabsorption Imaging Facility - VPIF

Padua -P Nicolosi and L Poletto

DCU - J Hirsch, K Kavanagh, E Kennedy & H de Luna

DESY ‘Pump Probe’ Project

Hasylab- J Feldhaus, E Ploenjes, K Tiedke, S Dusterer & R Treusch

Orsay-Michael Meyer, Denis Cubyannes & Patrick O'Keefe,

DCU-E Kennedy, P Yeates, J Dardis and P Orr (QUB)

'Colliding Plasmas'

DCU - K Kavanagh, H de Luna, J Dardis and M Stapleton

John t costello

Laser-Plasma/Atomic Phys-NCPST

The LPP node comprises 6 laboratory areas focussed on

pulsed laser matter interactions (spectroscopy/ imaging)

Academic Staff (4):John T. Costello, Eugene T. Kennedy (now VPR),

Jean-Paul Mosnier and Paul van Kampen (on sabbatical)

Post Doctoral Fesearchers (5):

Dr. Deirdre Kilbane (PVK/JC)

Dr. Hugo de Luna (JC)

Dr. Mark Stapleton (JC)

Dr. Jean-Rene Duclere (JPM)

Dr. Pat Yeates (ETK)

Current PhD students (6):

Caroline Banahan (PVK/JC)

Kevin Kavanangh (JC)

Adrian Murphy (JC)

John Dardis (JC)

Rick O'Hare (JPM),

Eoin O’Leary (ETK)

Visiting PhD students:Domenico Doria (Lecce) and Philip Orr (QUB)

Funded by:

SFI - Frontiers and Investigator

HEA - PRTLI and North-South

IRCSET - Embark & BRGS

Enterprise Ireland - BRGS

EU - Marie Curie and RTD

Part i laser plasma continua

Part I - Laser Plasma Continua

John t costello

Laser Plasma Source Parameter Range

Vacuum or

Background Gas





Laser Pulse 1064 nm/

0.01 - 1 J/ 5ps - 10 ns


Spot Size = 50 mm (typ.)

F: 1011 - 1014

Te : 10 - 1000 eV

Ne: 1021 cm-3

Vexpansion 106 cm.s-1

Emitted -





IR - X-ray Radiation

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What does a laser plasma look like ?

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Intense Laser Plasma Interaction

S Elizer, “The Interaction of High Power Lasers with Plasmas”,

IOP Series in Plasma Physics (2002)

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Laser Produced ‘Rare Earth’ Continua -

Physical Origin, History & Update

Laser plasma rare earth continua

Laser Plasma Rare Earth Continua

P K Carroll et al., Opt.Lett 2, 72 (1978)

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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 Trans- ition 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)

John t costello

But why is no line emission observed ?

  • Line emission is due to complex 4d-4f arrays in (typically) 7 - 20 times ionized atoms

  • 4dn5sq5ps4fm 4dn-15sr5pt 4fm+1, q+s = r+t

  • Furthermore 4f/5p and 4f/5s level crossing gives rise to overlapping bands of low lying configurations, most of which are populated in the ~100 eV plasma

  • Result - the summed oscillator strength for each 4d - 4f (XUV) and 5p - 5d (VUV) array is spread out over a supercomplex of transitions producing bands of unresolved pseudo continua (so called ‘UTA’) superimposed on the background continuum

  • Even expectedly strong lines from simple 4f - 4f arrays are washed out by plasma opacity

John t costello

There are up to 0.5 million allowed transitions in

LS couplingover the ~10 eV bandwidth of a UTA

In fact this is a lower bound since many additional LS forbidden transitions are ‘switched on’ by the breakdown in LS coupling here - G O’Sullivan et al., J.Phys.B 32, 1893 (1999)

John t costello

Brief History/ Highlights of Laser Plasma Rare-Earth’ Continua -1990

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)

7.XUV Reflectometer - S Nakayama et al., Physica Scripta 41, 754 (1990)

8.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 (1,2) and more recent work (3)

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)

3. E Kennedy et al., Radiat. Phys. Chem 70, 291 (2004)

John t costello

Recent Developments in LP Continua I


O Meighan et al., Appl.Phys.Lett 70, 1497 (1997)

O Meighan et al., J.Phys.B:AMOP 33, 1159 (2000)

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Summary - LP Continuum Light Sources

Table-top continuum light source now well established

Covers Deep-UV to soft X-ray spectral range

Pulse duration can be < 100 ps !

Continuum flux ~ 1014 photons/pulse/sr/nm (0.8J/10ns)

Low cost laboratory source - needs greater awareness

6.Recent work on (100 ps) + (6ns) Pre-plasma source -

we already see a flux gain of up to X4 with Cu-

A Murphy et al., Proc SPIE, 4876, 1202 (2003)

Problem of plasma debris for work in clean environments - proposals to solve, Michette, O’Sullivan, Attwood,…

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Part II- Dual Laser Plasma

Photoabsorption Experiments

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Part II - Section A

Photoabsorption Spectroscopy of Ions

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Photoionization of Atomic Ions

Still a lot of work to be done here-

Nice review by John West in:

J.Phys.B:AMOP 34, R45 (2001)

Covers DLP Experiments &

Merged Synchrotron + Ion Beams

John t costello

Dual Laser Plasma Principle






No tuning required

No vapour required

Backlighting Plasma Io

Both Plasmas I = Ioe-snL

Relative Absorption Cross Section

sNL =Ln(Io/I)

Isonuclear Sequences

Isoelectronic Sequences

Dx, DT, I(W/cm2)

 Species choice

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XUV DLP setup at DCU

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  • XUV DLP Specifications

  • Time resolution:~20 ns (LP Continuum duration)

  • Inter-plasma delay range:0 - 10 sec

  • Delay time jitter:± 1ns

  • Monochromator:McPherson™ 2.2m GI

  • X-VUV photon energy: 25 - 170 eV

  • Resolving power:~2000 @25 eV (20mm slits)

  • ~1200 @ 170 eV

  • Detector:Galileo CEMA with PDA readout

  • Spatial resolution:~250 m (H) x 250 m (V)

  • John t costello

    Some sample DLP case studies

    Kr-like ions

    Mn ions

    John t costello


    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+, Sr2+, Y3+

    John t costello

    Why Specifically Kr-like Ions ?

    Electronic Configuration


    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 ?

    John t costello

    XUV Photoabsorption along Isoelectronic (Kr-like) Sequence (Rostov/ DCU)

    4s24p6 + hnVUV 4s4p6np + 4s64p4nln’l’  Kr+(4s24p5) + e’l

    A Neogi et al., Phys.Rev.A 67, Art. No. 042707 (2003)

    P Yeates et al., J. Phys. B: At. Mol. Opt. Phys. 37, 4663 (2004)

    John t costello

    It's a plasma with an ionization balance-

    how do we know that we have Y3+ say ?

    4p - nd, Epstein and Reader , J. Opt. Soc. Am 72, 476 (1982)

    4s - 5p assigned using Clark et al., J. Opt. Soc. Am. B 3, 371 (1986)

    John t costello

    What could theory tell us ?



    John t costello

    What about

    cross sections ?

    John t costello

    'Mirroring Resonances'

    r2q2 0  complete cancellation - no resonances

    John t costello

    An update from Aarhus !

    Bizau, West & Kilbane (DCU)

    John t costello

    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 and

    that complex doubly excited resonances persist (at least in the early members

    of the isoelectronic sequence).

    2.Computed cross sections show good agreement with measured spectra.

    3.Rescaling the Coulomb interaction is needed to better fit the 4s-5p

    resonance in Sr2+

    4.We observe that the complex doubly excited resonances straddling the

    first 4s-5p in Kr moves to higher photon energy blending with higher energy

    4s-np (n>6) resonances and that the 4s-5p drops below the 4p threshold for Y3+

    For Y3+ the resonance q values become quite large and the spectrum

    consists mainly of almost symmetric absorption features

    We see that a number of features are suppressed in Rb+ and Sr2+ since

    they are built from exactly (or almost exactly) cancelling 'mirroring resonances'

    John t costello

    DLP XUV Photoabsorption along isonuclear

    sequences - Mn2+ (and Mn3+) Ions

    Mn+, 3p63d54s + hn  3p5(3d64s + 3d54s2)

    Mn2+, 3p63d5 + hn  3p5(3d6 + 3d54s)

    'duplicity of the 3d orbital' - "valence-like by energy but inner shell-like by radial distribution" (Dolmatov, JPB 29, L687 1996)

    John t costello

    3p-subshell photoabsorption - Mn2+

    John t costello

    3p-subshell photoabsorption - Mn2+

    Overall we see a good match with

    Dolmatov at least at the low energy

    side of the main resonance

    But why does the experimental

    trace fall off much more quickly

    than the theory -

    Excitation from metastable states ?

    John t costello

    Metastables and their effect on 3p-subshell

    photoabsorption of iron group ions - Mn3+

    Mn3+, 3p63d4 + hn  3p5(3d5 + 3d44s)




    John t costello

    What do simple Cowan code calculations give ?

    First Step

    Compute 'cross sections' for photoabsorption from ground and low-lying terms of Mn3+ (3d4) - 5D, 3P, 3F, 3G, and 3H

    John t costello

    What do you get ?

    John t costello

    Next Step

    To 'reproduce' the experimental plasma spectrum, take a weighted sum over each such cross section

    John t costello

    Vary the temperature and compare with expt.

    John t costello

    Mn ions - Summary

    Clear that we are going to have problems with excited state absorption

    since we have a hot sample. In fact the plasma temperature at will vary from

    ~10 eV at 20 ns to 2 eV at 150 ns and hence we will have significant

    populations of low lying 3dn and 3dn-14s states

    3.Same is also true of the ion beams used in the synchtotron experiments

    4.So we need a combined atomic physics and plasma physics approach

    -some codes available (HULLAC) but complex and expensive

    5.Contrast with Kr-like ions - closed shell - stable - ions tend to converge

    and stay on this favoured configuration - nice to work with

    Same problem will occur in 4d, 5d, 4f and 5f metals

    However, electronic structure of Mn2+ and Mn3+ ions important in

    manganites (recent Nature papers), biology (DNA),.....

    John t costello

    Part II - Section B (short)

    VUV Photoabsorption Imaging

    Collaboration between DCU & Univ. Padua

    John t costello

    VUV Absorption Imaging Principle

    Hirsch et al, J.Appl.Phys. 88, 4953 (2000) - QUB/DCU Collaboration






    Pass a collimated VUV beam through the plasma sample

    and measure the spatial distribution of the absorption. Convert

    to 'Equivalent Width' images and extract column density (NL)

    maps - see Rev.Sci. Instrum. 74, 2992 (2003) for details

    John t costello

    VUV Photoaborption Imaging

    • Time resolution: ~10 ns (200 ps - EKSPLA)

    • Spectral range:10 - 35 eV (120 - 35 nm)

    • VUV bandwidth:0.025 [email protected] eV (50mm slits)

    • Spatial resolution:~120 m (H) x 150 m (V)

    J Hirsch, E Kennedy, J T Costello, L Poletto & P Nicolosi

    Rev.Sci. Instrum. 74, 2992 (2003)

    John t costello

    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. Image analysis is not complicated by interference patterns

    since the VUVcontiuum source has a small coherence length

    4. VUV light can be used to photoionize ions -

    simplified equation of radiative transfer (no bound states).

    5. Fluorescence to electron emission branching ratio for inner

    shell transitions can be 10-4 or even smaller => almost all photons

    are converted to electrons

    John t costello

    VUV absorption Imaging- Ca+ - 33.2 eV

    3p64s (2S) - 3p54s3d (2P)

    John t costello

    Plume Expansion Profile -

    Singly Charged Calcium & Barium Ions

    Plume COG Position (cm)

    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

    John t costello

    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. Image analysis is not complicated by interference patterns

    since the VUVcontiuum source has a small coherence length

    4. VUV light can be used to photoionize ions -

    simplified equation of radiative transfer (no bound states).

    5. Fluorescence to electron emission branching ratio for inner

    shell transitions can be 10-4 or even smaller => almost all photons

    are converted to electrons

    John t costello

    What do we extract from I and Io images ?







    John t costello

    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+*(5p56s6d2P)  Ba2+ (5p61S)+e-

    h = 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

    John t costello

    Maps of equivalent width of Ba+ using

    the 5p-6d resonance at 26.55 eV (46.7 nm)

    John t costello

    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



    John t costello

    Result - Column Density [NL] Maps

    100 ns

    150 ns

    (C) 200 ns

    (D) 300 ns

    (E) 400 ns

    (F) 500 ns

    John t costello

    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

    John t costello

    Current & Future Applications

    Space Resolved Thin Film VUV Transmission

    and Reflectance Spectroscopy - PVK

    ‘Colliding-Plasma’ Plume Imaging

    Non-Resonant Photoionization Imaging

    VUV Projection Imaging ?

    Photoion Spectroscopy of Ion Beams ?

    John t costello

    Photoionization Mass Spectrometry

    R Flesch et al., Rev.Sci.Instrum 71, 1319 (2000)

    VUV Photoionizationof O2

    Laser on

    Laser off

    John t costello

    ‘Colliding Stars Model System' -

    'Colliding Plasmas'

    NGC2346 -

    Planetary Nebula

    Distance - 2,000 light years

    Extent ~ 0.4 light years

    Result of the collision of two stars - believed that one became a red giant

    and swallowed its partner in the binary system.

    Credit: Hubble Wide Field & Planeary Camera - Massimo Stiavelli (NASA)

    NGC 2346

    John t costello

    Colliding Laser Plasma Generation

    Laser Pulse Energy: 10 -150 mJ/ beam

    Laser Pulse duration:12 - 15 ns

    Focal Spot Size:~ 100 mm

    Irradiance: 1010 - 1011

    John t costello

    Ca - Emission Imaging @ 423 nm

    Stagnation for angled target geometry

    Tight point focus on each Ca face/ 120 mJ per beam

    John t costello

    How about hetero-atomic collisions ?

    - Li + Ca Plasmas

    • Should be able to track each plume species individually

    • so we could look for crossover at the stagnation layer









    John t costello

    Hetero-atomic collisions-Li+Ca Plasmas

    Ca -

    420 nm

    Ca+ -

    390 nm

    Li -

    670 nm

    Li+ -

    548 nm

    Delay = 300 ns & Gate time = 50 ns

    3O wedge, ~ 10mm Plume - Plume Separation

    John t costello

    'Collisionality Parameter'

    Collisionality (z) will be determined by both the mean free path

    (lii) and colliding plasma experimental scale length' (L).

    z = D/lii = D/Cstii = D.nii/Cs

    Cs= Ion sound speed,nii = ion-ion collision frequency

    Expect to strong stagnation for counter streaming plasmas

    where the mfp is small in comparison to the ablation front

    separation - Rambo and Denavit, Phys. Plasmas 1 4050 (1994)

    John t costello

    What have we learned to date ?

    Strong stagnation in table top colliding plasmas

    due to large value of the collisionality parameter (z)

    Degree of confinement/ hardness of the stagnation

    layer can be controlled by designing the value of z

    Stagnation layer becomes quite uniform after 100s ns

    and so looks attractive for investigation as alternative

    pulsed laser materials deposition source

    For this reason it also looks a good bet for atomic

    physics experiments using laser probing/excitation.....

    John t costello

    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)

    John t costello

    Free Electron Laser at

    Hasylab, DESY, Hamburg

    'Laser-like' radiation

    in the VUV and EUV

    John t costello

    Free electron radiation sources

    Josef Feldhaus, DESY, Hamburg

    Bending magnet, broad band

     NW x bending magnet

     NU2 x bending magnet


     NU2 x Ne x bending magnet

    NU , NW = # magnetic periods

    Ne = # electrons in a bunch

    John t costello

    Schematic layout of a SASE FEL

    LINAC Tunnel

    Experimental Hall

    John t costello

    Timetable EUV FEL - TTF2

    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

    John t costello

    Xe PES FEL (June 24th) - w, 2w & 3w

    John t costello

    Femtosecond X-VUV + IR

    Pump-Probe Facility,Hasylab, DESY


    John t costello

    Pump-probe experiments in the gas phase (project: II-02-037-FEL)

    M. Meyer et al, LIXAM, Orsay, France

    Participating groups:

    HASYLAB, Hamburg, Germany

    J. Feldhaus, S. Dusterer, R. Treusch, Kai Tiedke, Elke Ploenjes

    LIXAM, Orsay, France

    M. Meyer, D. Cubannes

    NCPST, Dublin City University, Ireland

    J. T. Costello, Philip Orr (QUB), P Yeates

    John t costello

    Two subsets of experiments


    Direct photoionization in a non-resonant laser field


    Resonant photoionization in a resonant laser field

    John t costello

    Let's first look at II-A -

    ‘Direct photoionization'

    in a non-resonant laser field*

    *Slides provided by Patrick O’Keefe and Michael Meyer,

    John t costello



    Ar+ 3p5


    Ar 3p6

    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)

    presence of IR:

    - shift of IP

    - broadening of PES peaks

    - sidebands

    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

    John t costello

    Cross correlation experiments using high order harmonics
















    Ekin (eV)



    (laser) = 800nm

    H11 = 17 eV

    H13 = 20 eV

    H15 = 23 eV




    E = 15.8 eV


    Ar+ 3p5


    Ar 3p6

    John t costello

    But also very interesting are:

    Type IIB-Experiments-

    'Resonant photoionization'

    in an intense/resonant fields

    =>Study intensity controlled autoionization !!

    John t costello

    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


    2s2p 1P – 2s3d 1D

    Intense Laser


    20 fs (34 meV)

    A. I. Magunov, I. Rotter and S. I. Strakhova

    J. Phys. B32, 1489 (1999)

    H. Bachau, Lambropoulos and Shakeshaft

    PRA 34, 4785 (1986)


    He 1s2

    John t costello

    Bachau, Lambropoulos and Shakeshaft, PRA 34, 4785 (1986)

    Laser on Resonance (d2 = 0)

    & scan the XUV photon energy

    1s2(1S) + hnXUV -

    {2s2p (1P) + hnLaser

    <=> 2s3d (1D)}

    John t costello

    Could this be done with a

    laser plasma X-VUV source

    and a table top OPA ?

    John t costello


    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

    John t costello

    But - the Ca+ 3p-subshell resonances have:

    1. Cross sections up to 2500 MB .vs. < 0.1MB for He

    2. Excitation widths up to 100 meV

    3. A VUV excitation energy (31 eV)

    John t costello

    Scheme- Ca+:

    3p64s (2S) + hnXUV (33.2 eV) 

    {3p53d4s (2P) + hnLaser (3 eV) <=> 3p53d5p (2D)}

    Exploratory study in DCU -

    Summer 2005

    John t costello

    Scheme- Ca+:

    John t costello

    Photoionization Summary

    Single VUV - X-ray photon photoionization (and concomitant

    correlation) in atoms and ions is still a rich source of physics

    Photoionization of atoms (much less so ions) in intense IR/VIS

    laser fields is now well established also (MPI .vs. Tunnelling)

    New things to so - 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 ?

    Pushing limits - exploring new spaces - new science & technol.

    John t costello

    Ideas that come to mind

    at this workshop

    FEL Opportunities

    PIFS on weak resonances

    PIFS on ion beams - Kr-like ions


    Exploring Xe-like, 5s-subshell excitation

    Table Top PIFS

    PIFS with laser plasma source

    Or with tuneable (upconverted) VUV

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