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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 www.physics.dcu.ie/~jtc & [email protected] .ie.

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slide1

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]

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

slide2

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
slide3

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

slide4

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

slide6

Laser Plasma Source Parameter Range

Vacuum or

Background Gas

Target

Plasma

Assisted

Chemistry

Laser Pulse 1064 nm/

0.01 - 1 J/ 5ps - 10 ns

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

slide8

Intense Laser Plasma Interaction

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

IOP Series in Plasma Physics (2002)

slide9

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)

slide11

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)

slide12

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
slide13

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)

slide14

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)

slide15

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)

slide16

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,…

slide17

Part II- Dual Laser Plasma

Photoabsorption Experiments

slide18

Part II - Section A

Photoabsorption Spectroscopy of Ions

slide19

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

slide20

Dual Laser Plasma Principle

Flexible

Neutral/

Multiplycharged/

Refractory

Elements

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

slide22

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)
slide23

Some sample DLP case studies

Kr-like ions

Mn ions

slide24

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+, Sr2+, Y3+

slide25

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 ?

slide26

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)

slide27

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)

slide29

What about

cross sections ?

slide30

\'Mirroring Resonances\'

r2q2 0  complete cancellation - no resonances

slide31

An update from Aarhus !

Bizau, West & Kilbane (DCU)

slide32

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\'

slide33

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)

slide35

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 ?

slide36

Metastables and their effect on 3p-subshell

photoabsorption of iron group ions - Mn3+

Mn3+, 3p63d4 + hn  3p5(3d5 + 3d44s)

Mn+

Mn2+

Mn3+

slide37

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

slide39

Next Step

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

slide41

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),.....

slide42

Part II - Section B (short)

VUV Photoabsorption Imaging

Collaboration between DCU & Univ. Padua

slide43

VUV Absorption Imaging Principle

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

VUV

CCD

Sample

Io(x,y,l,Dt)

I(x,y,l,Dt)

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

slide44

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)

slide45

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

slide46

VUV absorption Imaging- Ca+ - 33.2 eV

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

slide47

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

slide48

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

slide49

What do we extract from I and Io images ?

Absorbance:

l

Equivalent

Width:

dl

l

slide50

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

slide51

Maps of equivalent width of Ba+ using

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

slide52

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

dl

dl

slide53

Result - Column Density [NL] Maps

100 ns

150 ns

(C) 200 ns

(D) 300 ns

(E) 400 ns

(F) 500 ns

slide54

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

slide55

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 ?

slide56

Photoionization Mass Spectrometry

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

VUV Photoionizationof O2

Laser on

Laser off

slide57

‘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

slide58

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 W.cm-2

slide59

Ca - Emission Imaging @ 423 nm

Stagnation for angled target geometry

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

slide60

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

Li

Ca

Laser

Beam

Li

Wedge

Lens

Target

slide61

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

slide62

\'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)

slide63

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.....

slide64

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)

slide65

Free Electron Laser at

Hasylab, DESY, Hamburg

\'Laser-like\' radiation

in the VUV and EUV

slide66

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

slide67

Schematic layout of a SASE FEL

LINAC Tunnel

Experimental Hall

slide68

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

slide70

Femtosecond X-VUV + IR

Pump-Probe Facility,Hasylab, DESY

OPA

slide71

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

slide72

Two subsets of experiments

II-A

Direct photoionization in a non-resonant laser field

II-B

Resonant photoionization in a resonant laser field

slide73

Let\'s first look at II-A -

‘Direct photoionization\'

in a non-resonant laser field*

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

slide74

e-

IR

Ar+ 3p5

VUV

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

slide75

Cross correlation experiments using high order harmonics

H13

H15

H17

H19

H21

H23

50

DT

fs

0

-50

5

10

15

20

Ekin (eV)

Generation

(HHG)

(laser) = 800nm

H11 = 17 eV

H13 = 20 eV

H15 = 23 eV

:

:

IR

E = 15.8 eV

e-

Ar+ 3p5

VUV

Ar 3p6

slide76

But also very interesting are:

Type IIB-Experiments-

\'Resonant photoionization\'

in an intense/resonant fields

=>Study intensity controlled autoionization !!

slide77

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

2s2p 1P – 2s3d 1D

Intense Laser

2s2p

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)

VUV

He 1s2

slide78

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)}

slide79

Could this be done with a

laser plasma X-VUV source

and a table top OPA ?

slide80

Answer

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

slide81

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)

slide82

Scheme- Ca+:

3p64s (2S) + hnXUV (33.2 eV) 

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

Exploratory study in DCU -

Summer 2005

slide84

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.

slide85

Ideas that come to mind

at this workshop

FEL Opportunities

PIFS on weak resonances

PIFS on ion beams - Kr-like ions

DLP

Exploring Xe-like, 5s-subshell excitation

Table Top PIFS

PIFS with laser plasma source

Or with tuneable (upconverted) VUV

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