X-VUV Spectroscopy: A role for laser plasma light sources ? John T. Costello National Centre for Plasma Science & Technology (NCPST) and School of Physical Sciences, Dublin City University RAL-CLF Workshop on Applications Laser Plasma Generated X-rays, Jan

The Remit n Contribute to the discussion on a new (laser plasma) X-ray (X-VUV) source for the CLF Related question - Where do LPLS fit in the today’s ‘source value chain’ ?

Presentation Structure n The Centre for Laser Plasma Research (CLPR) Node of the NCPST: What do we do ? n DCU and the CLF: What have we done at RAL & why are we here today ? n What’s hot in At.Mol.Phys ? n Next generation experiments in photoionization n A new LPLS for (photoionization) at the CLF

NCPST/ CLPR - Who are we ? n NCPST established with Irish Government funding (Euro 8M) in Now EU Training Site. n Consortium of new and existing laboratories in plasma physics, chemistry and engineering n Fundamental and Applied Scientific Goals n CLPR node is divided into 4(6) laboratories focussed on PLD and photoabsorption spectroscopy/ imaging Staff: John T. Costello, Eugene T. Kennedy, Jean-Paul Mosnier and Paul van Kampen Postdocs: Dr. Amit Neogi, Dr. Mohamed Khater - 1 new EU and 1 new SFI Fellow PGs: John Hirsch, Kevin Kavanangh, Adrian Murphy (JC) Jonathan Mullen (PVK), Alan McKiernan, Mark Stapleton (JPM), Eoin O’Leary & Pat Yeates (ETK)

V-UV Photoabsorption Imaging Laboratory Project Title:VUV Photoabsorption Imaging*** Project Aim:To develop VUV photoabsorption imaging as a diagnostic of expanding plasma plumes (and other dynamic samples) Key Reference:J. Hirsch et al., JAP 88, 4953 (2000) & Rev.Sci.Instrum (submitted) DCU Personnel:John Hirsch, Kevin Kavanagh & John T. Costello Collaborators:Giorgio Nicolosi and Luca Poletto (Univ. Padua) First Experiment:RAL-CLF X-ray Laboratory 1999 Key Words: Plasma, Laser, Spectroscopy, Imaging, VUV Project Title:VUV Thin Film Imaging (DCU - AC Fellowship) Project Aim:Use the VPIF to perform transmission and reflection imaging and spectroscopy of thin films. DCU Personnel: Jonathan Mullen and Paul van Kampen

X-UV Spectroscopy Laboratory Project Title:Controlled Generation of Laser Plasmas Project Aim:Optical diagnostics of plasmas formed on non-planar target configurations (e.g., confined in capilliaries) in magnetic fields CLPR Personnel:Pat Yeates and Eugene T Kennedy Collaborators:J Lunney (TCD) Key Words: Plasma, Laser, Probe, Spectroscopy, XUV Project Title:Dual Laser Plasma Absorption Aim: Study of fundamentals of photoabsorption by ‘simple’ ions e.g., recently Kr-like ions (Rb + and Sr 2+ ) Key Reference:A Neogi et al., Phys.Rev.A (Submitted Dec. 02) CLPR Personnel:J T Costello, E Kennedy, J-P Mosnier and P van Kampen Collaborators:Gerry O’Sullivan (UCD) and Victor Sukhorukov (State Univ. Rostov)

V-UV Spectroscopy Laboratory Project Title:Analytical Characterisation of Steel Alloys Project Aim:VUV Laser Induced Plasma Spectroscopy Technique (VUV-LIPS) Record detection limits for C in Steel ( 2ppm !!) Key Reference:M A Khater, J T Costello and E Kennedy, Appl.Spec. 56, 970 (2002) CLPR Personnel: E O’Leary, M Khater, E T Kennedy and J T Costello, Key Words: Plasma, Laser, Analytical Spectroscopy, LIPS, VUV

Project Title:SXR Absorption Spectroscopy*** Project Aim:To extend the current Dual Laser Plasma Photoabsorption technique (XUV/ 20 ns) into the X-ray ( nm) and picosecond time domains. DCU Personnel: Adrian Murphy, Eugene Kennedy and John T. Costello Collaborators: Padraig Dunne/Gerry O’Sullivan (UCD) and Ciaran Lewis (QUB) First Experiment:RAL-CLF ASTRA 2002 Soft X-ray (SXR) Spectroscopy Laboratory (new) Key Words: Plasma, Laser, Point Projection Imaging, X-ray,

Pulsed Laser Deposition & Laser Ablation Diagnostics Lab(s) Project Title:Pulsed Laser Deposition Project Aim: PLD of GaN and ZnO. Laser Plasma Spectroscopy and Imaging is carried out at DCU to characterize the ablation mechanisms. Films are grown in TCD (soon DCU) and tested in DCU using 10K laser induced photoluminescence technique. Key Reference:K Mah et al., Appl. Phys. Lett 80, 3301 (2002) CLPR Personnel:Mark Stapleton, Alan McKiernan and Jean-Paul Mosnier Collaborators:D O’Mahony & J Lunney (TCD) / E McGlynn & M Henry (DCU) Key Words:PLD, Laser Ablation, Spectroscopy, Imaging VUV CCD

DCU and the RAL n Collaborated on 4 x EU-LSF Access Projects since 1995: 3 in the XR Lab and 1 at ASTRA n Work centred on development/ characterisation of picosecond XUV LPLS and their application in absorption spectroscopy/ imaging of LP plumes n CLF provides opportunities to access fast and ultrafast lasers in a flexible environment n ‘Pathfinder’ experiments, performed at the CLF, have underpinned success in levering Irish Government funds for new facilities at DCU

What’s hot in at. & mol. physics ? Ultra-cold Atomic BEC Ultracold Molecules and Collisions 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 X-VUV (c) Intense Optical + Intense X-VUV 3.Atoms, Molecules, Cluster & Ions in Intense Fields (Multiple-Photo and Optical Field-Ionization)

(a) Weak Optical + Weak X-VUV Experiment Type I

Photoionization of Laser Excited Species (Weak Optical + Weak X-VUV) “Investigation of Na 2p 5 3s3p resonances using angle resolved photoelectron spectroscopy of laser excited-aligned sodium atoms”, S Baier, M Schulze, H Staiger, P Zimmermann, C Lorenz, M Pahler, J Ruder, B Sonntag, J T Costello and L Kiernan, J.Phys.B:At.Mol.Opt.Phys 27, 1341 (1994) Experimental Setup Level Scheme

CIS (expt. & theor.) Angle Resolved PES

Can it be done at the XR Lab ?

Picosecond Dual Laser Plasma Photoionization at the CLF O Meighan, C Danson, L. Dardis, C L S Lewis, A MacPhee, C McGuinness R O’Rourke, W Shaikh, I C E Turcu and J T Costello, J.Phys.B:At.Mol.Opt.Phys 33, 1159 (2000) OPO/DYE

So type I (weak laser excitation) experiments appear straightforward with current laser technology

(b) Intense Optical + Weak X-VUV Experiment Type II

Photoionization of Atoms in Intense Fields - (Intense Optical + Weak X-VUV) 1. Bathe an atom in resonant X-VUV and optical fields e.g., He, Li (Hollow), Ca, Ca +, Ba, Ba +,….. He - 1s 2 ( 1 S) + h XUV -> {2s2p ( 1 P) + (intense)h Laser 2s3d ( 1 D)} 2. h Laser = eV (2 - 4 eV typ.) 3. Proposal around for a long time (Lambropoulos on He in1986) 4. No (?) experiments to date 5. Precursor to such experiments at VUV and X-FELs

Hollow Li (Field Free) 1s 2 2s( 2 S) + (weak) h XUV -> 2s 2 2p ( 2 P) “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 (1994) Satellite to 1st member of the famous Madden & Codling 2e series in He: 1s 2 ( 1 S) + (weak) h XUV -> 2s2p ( 1 P)

1s 2 2s( 2 S) + h XUV -> {2s 2 2p ( 2 P) + (intense)h Laser 2s 2 3d ( 2 D)} Theory- L Madsen, P Schlagheck and P Lambropoulos, PRL Vol 85, pp42-45 (2000) 1s 2 2s( 2 S) + (weak)h Laser -> 1s 2 2p ( 2 P) + (weak)h XUV -> 2s2p 2 ( 2 D) Laser-Excited Hollow Li Experiment - D Cubannes et al. PRL 77, 2194, (1996) Hollow Li in an intense laser field

L Madsen, P Schlagheck and P Lambropoulos, PRL Vol 85, pp42-45 (2000) Photoionization of Atoms in Intense Fields - Predictions

This is not an easy experiment ! In principle you just cross the sample with intense laser and weak XUV beams BUT The ‘Sample’ must be dilute - other wise RLDI will dominate and drive it into an ionized state Sample dilute => DLP photoabsorption experiment is unsuitable Can still use a laser plasma X-VUV source BUT Need wavelength selection and high (average) X-VUV intensity More sophisticated Photoion (or electron) spectroscopy needed Count rate low - ~ 1 ion/laser shot for He with V int ~ cm -3 !

But - the Ca & Ca + 3p-3d resonances have: 1. Cross sections up to 3000 MB.vs. < 1MB for Li 2. An excitation widths up to 100s meV 3. A VUV (normal incidence) excitation energy (31 eV) Scheme- Ca + : 3p 6 4s ( 2 S) + h XUV -> {3p 5 3d4s ( 2 P) + h Laser 3p 5 3d4p ( 2 D)} Possible collaboration with QUB on ion beam/TOF ? Many other possibilities - Ca, Ba, Sr, Na, K and their ions

What about the X-VUV source and tunable laser needed ?

A Laser-Plasma X-Ray Source for Photoionization at the CLF ? Wanted ! Reliable, Economical, Accessible, Flexible, ‘~10 ps’, High Rep. Rate, High Fluence/ High Average Power (tuneable)VUV - X-ray Source + Synchronised, high flux, tuneable (UV - IR) laser source (OPG ?) Desirable ! Good laser and plasma optical diagnostics suite + Full time laser support

Laser Specifications Laser (Plasma) Source 1. PRF: Hz (selectable) 2. Pulse energy: 500 mJ - 1 mJ (selectable) 3. Pulse duration: <10 ps - 50 ps (selectable) 4. Intensity: W.cm -2 (thermal X-rays) 5. X-VUV duration:< 100 ps 6. X-VUV tuning:Continuous, nm What might approaching this spec. right now ? “A pulse-train laser driven XUV source for picosecond pump-probe experiments in the water window” M Beck, U Vogt, I Will, A Liero, H Stiel, W Sandner and T Wilhelm, Opt. Comm. 190, pp (2001)

2 trains per second/ Micro-Pulses per train 15 mJ mJ per micropulse & 25 ps pulse duration XUV Pulse Duration (44 ps - Cu and 73 ps - PET) LP Source Details Experimental Setups Laser and XUV Pulse Trains XUV Spectra (line and continuum) Ph./1%/sr/train !! All Solid State !

What about ASTRA ? 1. Ideal for super-intense laser matter interactions - Up to W.cm -2 and really useful for testing ideas before full Vulcan PW experiments. 2. Generates HXR (Bremsstrahlung & K-alpha radiation) and HE particles - Many high end applications e.g., X and p- Radiography, relativistic effects in plasmas, …… Pre-compression (600 psec) beam (500 mJ) could be used to generate thermal X-rays. However EKSPLA 312P (1064 nm/ 500 mJ in 150 psec) costs < $75K and so calls into question whether this would be making best use of ASTRA ? 4. ASTRA PRF limited to 10 Hz - problem for ion counting!

Optical Source to Bathe Atoms in Intense Resonant Fields Parameters Wavelength Range:300 nm nm Pulse Duration:> X-VUV Duration Threshold (He/Li):<10 10 W.cm -2 Footprint:0.03 cm x 0.03 cm Peak Power:0.1 GW Tuneable Lasers Getting There ? OPO/DYE e.g., Continuum Panther mJ in 4 ns => GW or Continuum ND6000 (Powerlite 8010/532 nm) 200 mJ in 5 ns => 0.04 GW

But what about……..

(c) Intense Optical + Intense X-VUV ?

X-VUV FELs + Femtosecond OPAs- The Ultimate Photoionization Expt ? 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 (2004) 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 Key Reference: Personnel:MBI, DESY, CLPR-DCU, LURE, LLC, BESSY

Why the CLF XR Lab and not Diamond or 4 GLS ? ph./micropulse at G3 synchrotrons 2. Sci. & Tech. Transfer 3. Access (particularly FELs)

Before I forget ! Many thanks to all collaborators at the CLF XR Lab & at ASTRA TA2 for their commitment, advice, support and interest over the past years Summary coming up

Conclusions n Need VUV/XUV/X-ray source with shortest possible pulse width commensurate with providing high flux/pulse and high average power (continuously tunable) radiation n Must be flexible on pulse repetition rate x energy per pulse product ! n Combining with a high peak power tunable source opens up possibilities to study photoionization of a whole range of atoms, ions, etc. in weak and intense resonant fields for the first time n Good laser, laser plasma source and photoion diagnostics highly desirable