John T. Costello National Centre for Plasma Science & Technology (NCPST) and School of Physical Sciences, Dublin City University & VUV Photoabsorption Imaging QuAMP - Open University -September 8th 2003

Outline 1. ‘Centre for Laser Plasma Research’ /NCPST 2. VUV Photoabsorption/ionization Imaging Principle 3. ‘VPIF’ - VUV Photoabsorption Imaging Facility 4. Charge & State Selected Plasma Specie Images 5. Time Resolved Column Density Maps (Ba + ) 6. Conclusions and Current/Proposed Applications

NCPST/CLPR Who are we ? What do we do ?

NCPST What is it ? 1. NCPST established with Government/Benefactor funding (Euro 8M) in Now EU Training Site. 2. Consortium of new and existing laboratories in plasma physics, chemistry and engineering 3. Fundamental and Applied Scientific Goals

Staff: John T. Costello, Eugene T. Kennedy, Jean-Paul Mosnier and Paul van Kampen PDs:John Hirsch, D Kilbane (post Xmas) PGs: Kevin Kavanangh & Adrian Murphy (JC), Jonathan Mullen (PVK), Alan McKiernan & Mark Stapleton (JPM), Eoin O’Leary & Pat Yeates (ETK) MCFs:Jaoine Burghexta (Navarra) and Nely Paravanova (Sofia) Vacancies: PDRA-1: XUV FEL Experiments (ETK) PDRA-2: Pulsed Laser Deposition (JPM) PhD: Dual Laser Plasma Experiments (PVK/JC) The CLPR node comprises 5 (soon to be 6) laboratories focussed on PLD & photoabsorption spectroscopy/ imaging

NCPST/ CLPR - What do we do ? DCU Pico/Nanosecond Laser Plasma Light Sources VUV, XUV & (X-ray) Photoabsorption Spectroscopy VUV Photoabsorpion Imaging VUV LIPS for Analytical Purposes ICCD Imaging and Spectroscopy of PLD Plumes Orsay/Berkeley Synchrotrons Photoion and Photoelectron Spectroscopy Hamburg - FEL Femtosecond IR+XUV Facility Development

What’s a Laser-Plasma ?

How do you make a laser plasma ? Target Lens Laser Pulse- 1 J/ 10 ns Spot Size = 100  m (typ. Diam.)  > W.cm -2 T e = 100 eV (~10 6 K) N e = cm -3 V expansion  10 6 cm.s -1 Emitted - Atoms, Ions, Electrons, Clusters, IR - X-ray Radiation Plasma Assisted Chemistry Vacuum or Background Gas

What does a Laser Plasma look like ?

Intense Laser Plasma Interaction S Elizer, “The Interaction of High Power Lasers with Plasmas”, IOP Series in Plasma Physics (2002)

Part II - VUV Photoabsorption Imaging John Hirsch et al, Rev.Sci. Instrum. 74, 2992 (2003) POSTER P45 - Kevin Kavanagh

VUV Photoabsorption Imaging Principle Pass a collimated VUV beam through the plasma sample and measure the spatial distribution of the absorption. I o (x,y,,  t) Sample I(x,y,,  t) VUV CCD John Hirsch et al, J.Appl.Phys. 88, 4953 (2000)

Laser Plasma VUV/XUV Continua P K Carroll et al., Opt.Lett 2, 72 (1978) E T Kennedy et al., Opt.Eng 33, 3894 (1994)

Motivations 1. To add to the DCU Laboratory a new diagnostic to work alongside the existing spectroscopic systems 2. Pulsed Laser Deposition (PLD) and Dual Laser Plasma (DLP) photoabsortion expeiments require increasingly detailed knowledge of the spatio-temporal characteristics of plasma plumes 3. Lots of photoionization cross sections due (Aarhus/ALS) Limitations of existing imaging methods 1. Direct imaging of light emitted by a plasma using gated array detectors (e.g., ICCD) 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

Why a pulsed, tuneable and collimated beam ? Pulsed 1. Automatic time resolution: the VUV pulse ~ laser pulse duration (~15 ns) 2. By varying the delay between the lasers the plasma can be probed at different times after its creation Tuneable 3. One can access all resonance lines of all atoms and moderately charged ions with resonances between 30 nm and 100 nm Collimated 4. Light path identical for all rays: can derive the eqn of radiative transfer 5. The detector can be located far away from the sample plasma, reducing the ‘sample’ plasma signal on the detector, and improving SNR

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  3. The images analysis is not complicated by interference patterns since the VUVcontiuum source has a small coherence length (  ms) 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 or even smaller, almost all photons are converted to electrons Q. Anything Else ? A. Yes, it’s a VUV beam

VUV Photoabsorption Imaging Facility- ‘V-P-I-F’

The obligatory picture !!

Another one ! VUV Monochromator Mirror Chambers LPLS Chamber Sample Plasma Chamber VUV-CCD

VPIF - Design Considerations & Measured Characteristics

ParameterFocusing Toroid Collimating Toroid Entrance arm400 mm Exit arm400 mm- Tangential radius4590 mm9180 mm Sagittal radius34.9 mm63.5 mm Incidence angle85 degrees CoatingGold Mirror size60  20 mm Angle of acceptance10  10 mrad Final Design Parameters

VUV Photoabsorption Imaging Facility- Ray Tracing with ‘Light Path Simulation’ Computed point spread distributions at entrance slit for various apertures.

Ray Tracing with ‘Light Path Simulation’ Beam Footprints Computed and measured VUV beam footprints (A) 0.5m & (B) 1.0 m NOTE LOW DIVERGENCE !!

Wavelength (nm) Resolution He, 1s - 2p line 50  m/50  m slits R>1000 Wavelength (nm) Spectral Resolution at 54 nm ‘LPS’ Iint (Arb. Units)

Spatial Resolution (100  m/100  m slits & = 50 nm) Horizontal Plane (120  m) Vertical Plane (150  m)

VPIF Specifications Time resolution: ~20 ns (200 ps with new EKSPLA) Inter-plasma delay range:  sec Delay time jitter: ± 1ns Monochromator: Acton™ VM510 (f/12, f=1.0 m) VUV photon energy range: eV VUV bandwidth: eV (50  m/50  m slits) ~ nm Detector: Andor™ BN-CCD, 1024 x 2048/13  m x 13  m pixels Spatial resolution: ~120  m (H) x 150  m (V)

VUV Photoabsorption Imaging Principle Pass a collimated VUV beam through the plasma sample and measure the spatial distribution of the absorption. I o (x,y,,  t) Sample I(x,y,,  t) VUV CCD

What do we extract from I and Io images ? Absorbance: Equivalent Width: d

Io Equivalent Width (nm) W 1 - exp[-  NL] = 1 -I/Io = 1 -T

Some Preliminary Results: Tune system to 3 unique resonances Ca: 3p 6 4s 2 ( 1 S) - 3p 5 4s 2 3d ( 1 P) Ca + : 3p 6 4s ( 2 S) - 3p 5 4s 2 3d ( 2 P) Ca 2+ : 3p 6 ( 1 S) - 3p 5 3d ( 1 P) Time resolved W maps of Ca plume species

VUV Absorption Spectra of Ca Plasma Plumes

Maps of equivalent width of atomic calcium using the 3p-3d resonance at nm (31.4 eV)

Maps of equivalent width of singly ionized calcium using the 3p-3d resonance at nm (33.2 eV)

Maps of equivalent width of doubly ionized calcium using the 3p-3d resonance at nm (34.7 eV)

Plume Expansion Profile of Singly Charged Calcium Ions Ca + plasma plume velocity experiment: 1.1 x 10 6 cms -1 simulation: 9 x 10 5 cms -1 Ba + plasma plume velocity experiment: 5.7 x 10 5 cms -1 simulation: 5.4 x 10 5 cms -1 Delay (ns) Plume COG Position (cm)

Extracting maps of column density,e.g.,Barium We measure resonant photoionization, e.g., Ba + (5p 6 6s 2 S)+h   Ba + *(5p 5 6s6d 2 P)  Ba 2+ (5p 6 1 S)+e - h  = 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) Ergo ! We should be able to extract maps of column density - 'NL' = ∫n(l)dl

Maps of equivalent width of singly ionized Barium using the 5p-6d resonance at 46.7 nm

dl Convert from W E to NL Compute W E for a range of NL and fit a function f(NL) to a plot of NL.vs. W E Apply pixel by pixel d

Result - Column Density [NL] Maps (A)100 ns (B)150 ns (C) 200 ns (D) 300 ns (E) 400 ns (F) 500 ns

VPIF - Provides pulsed, collimated and tuneable VUV beam for probing dynamic and static samples Spectral, spatial, divergence etc. all in excellent agreement with ray tracing Recorded time and space resolved maps of equivalent width of Ca and Ba plasma species Extracted time and space resolved maps of column density for various time delays Measured plume velocity profiles which compare quite well with simple simulations based on self similar expansion Summary

Space Resolved Thin Film VUV Transmission and Reflectance Spectroscopy - PVK ‘Colliding-Plasma’ Plume Imaging Combining ICCD Imaging/Spectroscopy & PI Photoion Spectroscopy of Ion Beams ? Non-Resonant Photoionization Imaging Lots of new measurements from Aarhus & ALS Current & Future Applications

Collaborators - VPIF DCU John Hirsch Kevin Kavanagh Eugene Kennedy Univ. Padua Giorgio Nicolosi Luca Poletto Collaborators - Proof of RAL DCU John Hirsch et al QUB Ciaran Lewis Andy McPhee R O’Rourke RAL Graeme Hirst Waseem Shaikh

Ideally we would like a VUV/ XUV source with lots of photons to do these experiments !!

And there is one in Germany ! (and coming to the UK and US)

X-VUV FELs + Femtosecond OPAs- The Ultimate Photoionization Setup ? Tuneable:NOW! nm ( nm in 2004) Ultrafast:100 fs pulse duration High PRF: bunch trains/sec with up to 11315pulses/bunch Energy:Up to 1 mJ/bunch Intense:100  J (single pulse) /100 fs /1  m => W.cm -2 Moving to XUV (2005) and X-ray (2010): Need a Linac + insertion devices => Fraction of a GigaEuro !! Project Title: ‘Pump-Probe’ with DESY-VUV-FEL (EU-RTD) Aim:FEL + OPA synchronisation with sub ps jitter URL: Personnel:MBI, DESY, CLPR-DCU, LURE, LLC, BESSY

Femtosecond X-VUV + IR Pump-Probe Facility,Hasylab, DESY DESY, MBI, LURE, BESSY, LLC & NCPST-DCU