John T. Costello National Centre for Plasma Science & Technology (NCPST) and School of Physical Sciences, Dublin City University & Laser Generated Plasmas - (Stars with a Bright Future) Astronomy/Phys Society, NUI-Maynooth, Feb 17th, 2004

Outline of Talk Part I - Laser Plasma Fundamentals n Laser Plasmas: Generation, Properties & Scales Part II - Laser Plasma UV - X-ray Light Sources Part III - Absorption Imaging of Laser Plasmas Part IV - Into the future Laser Plasmas & Extreme Physics Ultraintense (Petawatt) Laser Generated Plasmas - RAL A New Laser, 'VUV/X-Ray Free Electron Laser' - DESY-FEL

Collaborators & Contributors to the Talk Laser Plasma Sources RAL - Edmund Turcu & Waseem Shaikh QUB - Ciaran Lewis and A MacPhee DCU - Oonagh Meighan & Adrian Murphy Absorption Imaging Padua -Piergiorgio Nicolosi and Luca Poletto DCU - John Hirsch, Kevin Kavanagh & Eugene Kennedy DESY Extreme-UV & X-ray Free Electron Laser Hasylab- Josef Feldhaus, Elke Ploenjes, Kai Tiedke et al. Orsay-Michael Meyer & Patrick O'Keefe, Lund-Jorgen Larsson et al. MBI-Ingo Will et al. DCU-Eugene Kennedy & John Hirsch Padua-Piergiorgio Nicolosi Petawatt VULCAN LaserVUV/EUV Science & Technology RAL - Colin DansonU. Berkeley - David Attwood

Staff: John T. Costello, Eugene T. Kennedy, Jean-Paul Mosnier and Paul van Kampen Post Doctoral Fellows: John Hirsch (ETK/JC) Deirdre Kilbane (PVK/JC) Jean-Rene Duclere (JPM) Incoming - Hugo de Luna (JC) - Easter 2004 Vacancy (ETK) PGs: Kevin Kavanangh, Adrian Murphy (JC) Jonathan Mullen (PVK) + Vacancy (PVK/JC) Alan McKiernan, Mark Stapleton, Rick O'Hare (JPM), Eoin O’Leary & Pat Yeates (ETK) MCFs: Jaoine Burghexta (Navarra) and Nely Paravanova (Sofia) Michael Novotny (CZ - incoming) The CLPR node comprises 6 laboratories focussed on PLD (2) & photoabsorption spectroscopy/ imaging (4) NCPST - CLPR

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

Part I - Table Top Laser-Plasmas

Plasma & The 4 Phases of Matter Greek PhilosophersPhysicists Earth Solid Water Liquid Wind Gas FirePlasma Plasma: Fluid (gas) of electrons and ions

Why study plasmas ? NGC 4676 Plasma Process ? START

'Table-Top' Pulsed Lasers Q-switched Nd-YAG: DCU 1J in 10 ns = 100 MW, (10 12 W.cm -2 in 100  m spot) SBS Compressed Nd-YAG: DCU 0.5J in 150 ps ~ 3 GW, (10 14 W.cm -2 in 30  m spot) Modelocked Ti-Sapphire: Coherent (QUB-PLIP) 0.03 mJ in 30 fs = 1 GW, 1 x W.cm -2 in a 10  m spot

How do you make a laser plasma ? Target Lens Emitted - Atoms, Ions, Electrons, Clusters, IR - X-ray Radiation Plasma Assisted Chemistry Vacuum or Background Gas Laser Pulse 1064 nm/ J/ 5ps - 10 ns Spot Size = 50  m (typ.)  : W.cm -2 T e : eV N e : cm -3 V expansion  10 6 cm.s -1

How is a laser plasma formed ? n Seed electrons are liberated by single (or multi) photon ionization from the surface forming a tenuous plasma n These electrons absorb laser photons by Inverse Bremssstrahlung (IB) and are raised to high energies - e (T1) + n  + (Z n+ )  e (T2) + (Z n+ ), T2 = T1+nЋ  n These energetic electrons collide with the target surface causing futher ablation and ionization. The electron density close to the target surface rises rapidly until a 'critical density layer' is formed where the 'plasma frequency' becomes comparable to the laser frequency,  P =  Laser -  P =(4  e 2 n e /m e ) 1/2,  Laser =(4  e 2 n c /m e ) 1/2 - n c (cm -3 ) = 1.1 x (1  m/ Laser) 2 n At this point the plasma becomes reflecting and the laser light cannot penetrate through ot the target. n The Plasma plume expands, n e drops below n c, the laser light penetrates through to the surface and the process cycle continues.

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

What does a Laser Plasma look like ?

Video - Air Breakdown with 150 picosecond laser pulses

Video - Air Breakdown with 150 picosecond laser pulses - EKSPLA 312P

Plasma temperatures, expansion velocities, etc. all easily estimated from simple scaling laws - See Shalom Elizer,' 'The interaction of high power lasers with plasmas' IOP Publishing, 2002 Reviewed by J Costello in 'Contemporary Physics', Vol 44, pp (2003) Laser Plasmas - Some Fundamentals The state of a plasma is characterised by e.g., electron temperature, average ion stage, etc.

Laser Plasmas  Electron Temperatures Plasma Electron Temperature T e - dependence on laser wavelength & intensity D Colombant & G F Tonon, J.Appl.Phys Vol 44, pp (1973)

Laser-Plasmas  Extreme Plasma Fields

Laser-Plasmas  Extreme Plasma Pressure

How highly charged can the ions get ?

Laser Plasmas  Plume Velocity

Essentially a fast framing camera - Nanosecond shutter time & synchonised to laser with low (<ns) jitter ! Plasma plume expands rapidly  need fast (nanosecond) time resolved probes and detectors Solution: Intensified CCD - (ICCD)

Time Resolved (gated) ICCD imaging I ICCD tt Delay-Gate Gen. Nd-YAG 0.5 J/ 15 ns

Videos of plume emission of laser plasma expanding into vacuum. Each frame is 10 ns wide/ 50 ns delay between frames Video 1 Video 2 ICCD Framing Photography (P Yeates, DCU)

Video 1 - Laser Plasma formed on flat Al metal surface

Video 2 - Laser Plasma formed in slot (confined)

So, in summary we know that: Laser Produced Fireballs are- Hot: T e = Kelvin Dense: n e = e/cm 3 Transient:ps -  s Rapid: cm/sec Dublin to Cork in 3 seconds !!!

We can tune temperature, density etc. so that they produce spectra to be compared with spectra from other laboratory and astrophysical sources !! So now we know that laser plasmas are hot & dense ! Laser - Astrophysical Plasmas - Solar Interior Figure - David Attwood, U C Berkeley

Part II- UV to X-ray Light Sources Generally Extreme-UV Science & Technology is Growing Rapidly 1.Industry: Lithography 2.Bio-Medical: Microscopy 3.Basic Research: Astronomy

Since a laser plasma is HOT - (T e = eV) and (say) you consider it to be a black (or grey) body, then most emission should be at photon energies also in the eV range, i.e., at Vacuum Ultraviolet (VUV), Extreme-Ultraviolet (EUV) and Soft X-ray (SXR) wavelengths !! Figure from lectures notes of David Attwood, U Calif.-Berkeley Laser Plasmas as VUV to X-ray Light Sources - I

Lots of activity right now driven by prospects for reducing feature sizes in semiconductor lithography - diffraction limit Lithography Slides from David Attwood - Berkeley Laser Plasmas as VUV to X-ray Light Sources - II

EUV Solar Image using a Multilayer Mirror based Cassegrain Mount From Lectures Notes of Prof. David Attwood, U Calif.-Berkeley TRACE Image Arthur B C Walker: Born: Aug.24, 1936 Died: Apr.29, 2001 sunland.gsfc.nasa.gov/smex/trace/ EUV- SXR astronomy

But back to laser-plasma EUV Sources

Our Major Objective: We want to probe matter with wavelength tuneable UV-SXR radiation so that we can study photoabsorption/ photo- ionization. Ergo we need a laser plasma source that emits a 'continuum' from the UV to the soft X-ray: We need a table-top 'synchrotron'

P K Carroll et al., Opt.Lett 2, 72 (1978) Laser Produced ‘Rare Earth’ Continua Physical Origin, History & Update

What is the Origin of the Continuum ? Continua emitted from laser produced rare-earth (and neighbouring element) plasmas are predominantly free-bound in origin Where have all the lines gone ? Bound - Free Transitions - Recombination/Photoionization* A (n+1)+ + e  A n+ + h

Ultrafast Laser Plasma Continua - I Picosecond LPLS (DCU, QUB & RAL, UK) Meighan, Costello et al., Appl.Phys.Lett 70, 1497 (1997) & J.Phys.B 33, 1159 (2000)

Streak Camera Trace from a W plasma Picosecond EUV Emission Spectra Ultrafast Laser Plasma Continua - II

Summary - LP Continuum Light Sources 1.Table-top continuum light source now well established 2.Covers Deep-UV to soft X-ray spectral range 3.Pulse duration can be < 100 ps ! 4.Continuum flux ~ photons/pulse/sr/nm 5.Low cost laboratory source 6.Next step - Working 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)

Now we can probe matter with photoionizing radiation from this Fast-Pulsed, Laser Plasma Continuum Light Source

BUT !!! Laser plasmas are also are a source of atoms, ions, clusters, etc. Ergo not only should we be able to develop laser plasmas into light sources but also into samples of atoms and ions to be probed. Result - DUAL LASER PLASMA (DLP) PHOTO-ABSORPTION EXPERIMENTS

DUAL LASER PLASMA (DLP) EXPERIMENTS UV - Xray Source Absorbing Sample

Why Photoabsorption ?  Access to ground/ metastable state (Dark) species  Electric dipole excitation yields tractable spectra

Photoabsorption/ ionization data are relevant to-  Astrophysical spectra and models  Laboratory plasma modelling  Fundamental many-body theory  X-ray laser schemes  ICF

DLP Studies on C Ions (Padua)- I VUV Photoabsorption - Absolute Cross-sections ! Normal Incidence DLP Setup P Recanatini, P Nicolosi & P Villoresi, Phys. Rev. A 64, Art. No (2001) Spaced resolved emission from a W plasma in the VUV around (a) 49 nm and (b) 69 nm Motivation: Ions of astrophys. interest, tests of databases (Opacity, etc.)

DLP Studies on Ions (Padua) - II, C + Absorption spectra of C+ taken at an inter-plasma delay of 58 ns and at 2.1 and 3.3 mm above the carbon target surface 2.1 mm 3.3 mm 1.2 J on target in line focus: 9 mm X 0.01 mm

Work centres low-Z ions of astrophysical interest All isonuclear sequences of Be, B and C measured. Designed and built DLP systems to work from VUV to Soft X-ray (Carbon K) Have determined absolute photoabsorption cross sections using DLP Group have designed and built many VUV and EUV spectrometers and optical systems for NASA Summary - Padua

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 ! Recent Examples “Trends in Autoionization of Rydberg States converging to the 4s Threshold in the Kr-Rb + -Sr 2+ Series: Experiment and Theory” Amit Neogi, John T Costello et al., Phys.Rev.A 67, Art. No (2003) “EUV Ionising Radiation and Atoms and Ions: Dual Laser Plasma Investigations”, E T Kennedy, J T Costello, J-P Mosnier and P van Kampen, Radiat. Phys. Chem. (in press 2004)

BUT NO TIME TO TALK ABOUT THAT RIGHT NOW BECAUSE I WANT TO TALK ABOUT

VUV Photoabsorption Imaging Part III Collaboration between DCU & Univ. Padua Key paper: J Hirsch, E Kennedy, J T Costello, L Poletto & P Nicolosi Rev.Sci. Instrum. 74, 2992 (2003)

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)

Why Photoabsorption ? Because we can see the 'Dark' or 'Non-Emitting' matter in the plasma Direct imaging of light emitted by a plasma using gated array detectors (e.g., ICCD) provides information on excited species only

Why a pulsed, tuneable and collimated beam ? Pulsed Automatic time resolution: the VUV pulse duration ~ laser pulse duration (~ ns) Wavelength Tuneable Can access all resonance lines of all atoms & moderately charged ions with resonances between 30 nm and 100 nm (present system) Collimated (Parallel VUV Beam) Can place the sample and CCD anywhere along the beam

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

The obligatory picture !! VUV Monochromator Mirror Chambers LPLS Chamber Sample Plasma Chamber VUV-CCD

VPIF Specifications Time resolution: ~10 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 ( nm) 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)

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

Tune system to 3 unique resonances Ca: 3p 6 4s 2 ( 1 S) +  (31.4 eV)  3p 5 4s 2 3d ( 1 P) Ca + : 3p 6 4s ( 2 S) +  (33.2 eV)  3p 5 4s 2 3d ( 2 P) Ca 2+ : 3p 6 ( 1 S) +  (34.7 eV)  3p 5 3d ( 1 P) Time resolved W maps of Ca plume species

Maps of equivalent width of atomic calcium using the 3p-3d resonance at 31.4 eV (39.48 nm) mJ on line focus 3mm x mm

Maps of equivalent width of Ca + using the 3p-3d resonance at 33.2 eV - (200 mJ/15ns on line focus 5 mm x mm)

Maps of equivalent width of Ca 2+ using the 3p-3d resonance at 34.7 eV mJ/15ns on line focus 5mm x mm

Expansion of singly ionized calcium plume component using the 3p-3d resonance at nm (33.2 eV) 7 frames: 5 ns, 20 ns, 35 ns, 50 ns, 75 ns, 100 ns &125 ns 4 mm PLD Fluence level - 40 mJ/mm 2 or 4J/cm 2

Plume Expansion Profile of Singly Charged 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)

You can also extracts maps of column density, e.g.,Singly Ionized Barium Since 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) We should be able to extract maps of column density - 'NL' = ∫n(l)dl

Maps of equivalent width of Ba + using the 5p-6d resonance at eV (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 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 (1000) & spatial (<100  m) 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 VPIF - Summary

Space Resolved Thin Film VUV Transmission and Reflectance Spectroscopy - PVK ‘Colliding-Plasma Plume' Imaging Combining ICCD Imaging/Spectroscopy & P/Imag Non-Resonant Photoionization Imaging VUV Projection Imaging ? Photoion Spectroscopy of Ion Beams ? Current & Future Applications

‘Colliding Stars Model System' - 'Colliding Plasmas' NGC 2346

First and very preliminary tests on colliding plasma imaging with the VPIF

Colliding Plasmas on Flat Target

Colliding 'Opposing' Plasmas

Part IV - Into the future Laser Plasmas & Extreme Physics Ultraintense (Petawatt) Laser Generated Plasmas - RAL A New Laser, 'VUV/X-Ray Free Electron Laser' - DESY-FEL

Petawatt 'VULCAN laser' - RAL-UK 800 J in 800 fs = 1 PW, W.cm -2 in a 10  m spot

Extreme Fields - Accelerated Plasma Electrons When do the electrons (plasmas) go relativistic ?  = 30 - v e =0.999 c

1.So already we have electrons accerated up to GeV energies over a laser plasma dimension of < 0.1 mm 2.So the possibility for compact GeV and maybe even TeV accerators cannot be ruled out 3.Also high fluxes of > 10 MeV ions, neutrons/protons have been produced and even proton radiographs !! M Borghesi (QUB)

Free Electron Laser at Hasylab, DESY, Hamburg 'Laser-like' radiation in the VUV and EUV And Finally !!!!!!

Free electron radiation sources Bending magnet, broad band  N W x bending magnet  N U 2 x bending magnet  N U 2 x N e x bending magnet N U, N W = # magnetic periods N e = # electrons in a bunch 1 = u /2  2 (1+K 2 /2) Josef Feldhaus, DESY, Hamburg

Schematic layout of a SASE FEL

First Experiments DESY Phase 1 FEL Nature 420 (2002) 482

The DESY (EUV) FEL will generate low temperature and high density plasmas - WARM DENSE MATTER

Dual Laser Experiments at the Hamburg (Hasylab), DESY - FEL EUV FEL + Femtosecond OPAs- The Ultimate Photoionization Expt ? Tuneable:TTF1: nm 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 Project Title: ‘Pump-Probe’ with DESY-VUV-FEL (EU-RTD) Aim:FEL + OPA synchronisation with sub ps jitter Key Ref: Personnel:DESY, MBI, CLPR-DCU, LURE, LLC, BESSY

synchronization nm 100 fs SHG Nd:YLF pulse train laser (identical to cathode laser) pump beam 524 nm 10 ps Ti-Sa oscillator LBO crystal Non-linear crystal OPA Amplified beam Filter Synchronization with RF/FEL Pulse stretcher Pulse compressor 10 ps nm 150 fs weak tunable femtosecond high-power 1048 nm 10 ps Laser system developed by MBI Transport to DESY early 2004 Two- color pump-probe facility combining a FEL and a high-power optical laser EU FP5 Project Participating Organisations HASYLAB at DESY, Germany (coord.) BESSY GmbH, Germany Max-Born-Institut Berlin, Germany Dublin City University, Ireland MAX-Lab, Lund Laser Centre, Sweden CNRS/LURE Orsay, France Goal: 200 fs

Two- color pump-probe facility combining a FEL and a high-power optical laser We will be able to study intense laser-matter interaction at ultrashort laser wavelengths (1nm) for the first time We will be able to do new photoionization experiments on laser generated plasmas (WDM), clusters etc. with femto- second time resolution The unprecedented intensity will permit detection and measurements of weakly absorbing species We will be able to do non-linear optics (e.g., harmonic generation, IR + EUV frequency mixing) in the EUV and X-ray for the first time

Time table EUV FEL 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

European XFEL – Site Proposal

Thank you for listening !!! Conclusions n Large body of knowledge built up since the first laser plasma experiments of the mid. 1960s n Laser Plasmas are poised (much like discharge plasmas 20 years ago) to have a major industrial/Biomedical impact: Pulsed Laser Deposition (didn't mention) but also as VUV - X-ray light sources n VUV, EUV& X-ray optics developing rapidly and will match UV/visible optics in the next decade n Ultrafast, Petawatt and EUV lasers will bring us into new parameter spaces (some dovetailing with astrophysical plasmas) where we can explore extreme physics