X-VUV Spectroscopy: A role for laser plasma light sources ?

John T. CostelloNational 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 14 - 2003

The Remit

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

The Centre for Laser Plasma Research (CLPR)

Node of the NCPST: What do we do ?

DCU and the CLF: What have we done at RAL

& why are we here today ?

What’s hot in At.Mol.Phys ?

Next generation experiments in photoionization

A new LPLS for (photoionization) at the CLF

NCPST/ CLPR - Who are we ? NCPST established with Irish Government funding

(Euro 8M) in 1999. Now EU Training Site. Consortium of new and existing laboratories in

plasma physics, chemistry and engineering Fundamental and Applied Scientific Goals 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. CostelloCollaborators: 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 PlasmasProject 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 AbsorptionAim: Study of fundamentals of photoabsorption by ‘simple’ ions e.g.,

recently Kr-like ions (Rb+ and Sr2+)

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 (0.2 - 2nm) 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 MosnierCollaborators: D O’Mahony & J Lunney (TCD) / E McGlynn & M Henry (DCU)

Key Words: PLD, Laser Ablation, Spectroscopy, Imaging

VUVCCD

DCU and the CLF @ RAL

Collaborated on 4 x EU-LSF Access Projects since 1995: 3 in the XR Lab and 1 at ASTRA

Work centred on development/ characterisation of picosecond XUV LPLS and their application in absorption spectroscopy/ imaging of LP plumes

CLF provides opportunities to access fast and ultrafast lasers in a flexible environment

‘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 Fields1. 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 2p53s3p 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 SetupLevel 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 - 1s2 (1S) + hXUV-> {2s2p (1P) + (intense)hLaser <-> 2s3d (1D)}

2. hLaser = 3.574 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)

1s22s(2S) + (weak) hXUV-> 2s22p (2P)

“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)

Satellite to 1st member of the famous Madden & Codling 2e series in He:1s2(1S) + (weak) hXUV-> 2s2p (1P)

1s22s(2S) + hXUV-> {2s22p (2P) + (intense)hLaser <-> 2s23d (2D)}

Theory- L Madsen, P Schlagheck and P Lambropoulos, PRL Vol 85, pp42-45 (2000)

1s22s(2S) + (weak)hLaser-> 1s22p (2P) + (weak)hXUV -> 2s2p2 (2D)

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 Vint ~ 10 -3 cm-3 !

But - the Ca & Ca+ 3p-3d resonances have:

1. Cross sections up to 3000 MB .vs. < 1MB for Li2. An excitation widths up to 100s meV3. A VUV (normal incidence) excitation energy (31 eV)

Scheme- Ca+:

3p64s (2S) + hXUV-> {3p53d4s (2P) + hLaser <-> 3p53d4p (2D)}

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 SpecificationsLaser (Plasma) Source1. PRF: 1 - 1000 Hz (selectable)2. Pulse energy: 500 mJ - 1 mJ (selectable) 3. Pulse duration: <10 ps - 50 ps (selectable)4. Intensity: 1012 - 1015 W.cm-2 (thermal X-rays)5. X-VUV duration: < 100 ps6. X-VUV tuning: Continuous, 0.1 - 100 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, pp317-326 (2001)

2 trains per second/ 25 - 400 Micro-Pulses per train15 mJ - 0.5 mJ per micropulse & 25 ps pulse durationXUV Pulse Duration (44 ps - Cu and 73 ps - PET)

LP Source Details

Experimental Setups Laser and XUV Pulse Trains

XUV Spectra (line and continuum)

1011 Ph./1%/sr/train !!All Solid State !

What about ASTRA ?1. Ideal for super-intense laser matter interactions - Up to 1019 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, ……...

3. 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

ParametersWavelength Range: 300 nm - 600 nmPulse Duration: > X-VUV DurationThreshold (He/Li): <1010 W.cm-2

Footprint: 0.03 cm x 0.03 cmPeak Power: 0.1 GW

Tuneable Lasers Getting There ? OPO/DYEe.g., Continuum Panther - 100 mJ in 4 ns=> 0.025 GW orContinuum 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! 80 - 110 nm (20 - 60 nm in 2004)Ultrafast: 100 fs pulse durationHigh PRF: 1 - 10 bunch trains/sec with up to 11315pulses/bunchEnergy: Up to 1 mJ/bunchIntense: 100 J (single pulse) /100 fs /1 m => 1017 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: http://tesla.desy.de/new_pages/TDR_CD/start.htmlPersonnel: MBI, DESY, CLPR-DCU, LURE, LLC, BESSY

Why the CLF XR Lab and not Diamond or 4 GLS ?

1. 105 - 108 ph./micropulse at G3synchrotrons2. Sci. & Tech. Transfer3. 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 Need VUV/XUV/X-ray source with shortest possible

pulse width commensurate with providing high flux/pulse

and high average power (continuously tunable) radiation

Must be flexible on pulse repetition rate x energy per

pulse product !

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

Good laser, laser plasma source and photoion

diagnostics highly desirable