John T. Costello National Centre for Plasma Science & Technology (NCPST)/ School of Physical Sciences, Dublin City University Two Colour and Two Photon Ionization Processes in Intense XUV and Optical Fields at FLASH UXSS - SLAC. June 18, 2009 ' FLASH ' - Free Electron LASer in Hamburg

LIXAM (Orsay): D. Cubaynes, M. Meyer Universite Paris 06 (PMC): R. Taieb, A. Maquet DESY (Hamburg): A. Azima, S. Düsterer, P. Radcliffe, H. Redlin, W-B Li, J. Feldhaus PTB (Berlin): A. A. Sorokin, M. Richter Moscow State University: A. N. Grum-Grzhimailo, E. V. Gryzlova, S. I. Strakhova Queen’s University Belfast: Hugo van der Hart Dublin City University: J. Dardis, P. Hayden, P. Hough, T. Kelly, V. Richardson, E. T. Kennedy, J. T. Costello Thanks to AG Photon (R Treusch et al.) & AG Machine (M Yurkov et al.) Acknowledgements UXSS - SLAC. June 18, 2009

DCU Intense Laser Matter Research Academic Staff (5): John T. Costello, Eugene T. Kennedy, Jean-Paul Mosnier, Lampros Nikolopoulos and Paul van Kampen Current Postdocs (2): Dr. Patrick Hayden, Dr. Sateesh Krishnamurty (Incoming - Subhash Singh) Current PhD students (13 + 1): John Dardis, Jack Connolly, Brian Doohan, Colm Fallan, Padraig Hough, Eanna Mac Carthy,, Mossy Kelly, Conor McLaughlin, Ricky O'Haire, Vincent Richardson, Dave Smith, Tommy Walsh & Jiang Xi, open position (with LN) Recent PhD Graduates: Caroline Banahan, Mark Stapleton, Jonathan Mullen, Kevin Kavanagh, Eoin O’Leary Recent Postdocs: Deirdre Kilbane, Hugo de Luna, Jofre Gutieriez-Pedrogosa, Brendan Doggett, Subo Chakraborti and Jean-Rene Duclere 6 laboratory areas focussed on pulsed laser matter interactions (NIR – X-ray/ 30fs – 30 ns, spectroscopy/ imaging/PLD) Funded by: SFI - Frontiers and Investigator HEA – PRTLI (Kit) IRCSET (People) EU - Marie Curie (People) UXSS - SLAC. June 18, 2009

DCU Intense Laser Matter Research UXSS - SLAC. June 18, 2009 Research Domains: Photoionization of Atoms and Ions with Laser Plasma, Synchrotron and Free Electron Laser Light Sources (JC, PVK, ETK, LN) Optical Diagnostics of Laser Produced Plasmas (JC) Laser Induced Breakdown Spectroscopy – LIBS (JC, ETK) Pulsed Laser Deposition (PLD) of Materials (JPM) Some Current Projects: Two colour photoionization of atoms with XUV FELs (& LPLS) UV-Vis imaging, spectroscopy and interferometry of colliding laser produced plasmas (with Sivandan ‘Hari’ Harilal, Purdue) Colliding plasma targets for EUVL light sources (with UCD & TCD) VUV-LIBS for Elemental Characterisation in Steel PLD and in-situ P-type doping of ZnO nanostructures 6 laboratory areas focussed on pulsed laser matter interactions (NIR – X-ray/ 30fs – 30 ns, spectroscopy/ imaging/PLD)

Collaboration grew out of EU RTD Project: HRPI-CT Title:“X-Ray FEL Pump Probe Facility” Partners: Orsay, DCU, Lund, MBI, BESSY & DESY Collaboration - Origin UXSS - SLAC. June 18, 2009

1.Few-photon single and multiple ionization processes 2.Ultra-dilute targets 3.Photo-processes with ultralow cross-sections 4.Pump and probe experiments (XUV + XUV or XUV + Opt.) 5.Single shot measurements 6.Brings inner-shell electrons into non-linear processes 7.Re-asserts primacy of the photon over field effects* ! What are the USPs of XFELs in AMOP ? UXSS - SLAC. June 18, 2009 *See USP No. 1

FLASH (Brief) Overview Atoms in Intense XUV + NIR Fields 1. Coherent Photoionization Processes in Superposed Fields 2. Few Femtosecond X-ray Photoionization Processes at LCLS Two Photon Ionization in Intense XUV Fields Next Steps Outline of the Talk UXSS - SLAC. June 18, 2009

Part 1 - FLASH Overview UXSS - SLAC. June 18, 2009

300 m FLASH Overview Energy range: ~ 0.3 – 1 GeV     ~ 6.5 – 60 nm Laser Bunch Compressor Bypass Undulators Collimator Bunch Compressor 5 MeV127 MeV450 MeV1000 MeV Accelerating StructuresDiagnostics FEL Diagnostics RF-gun UXSS - SLAC. June 18, 2009

water window Wavelength range (fundamental): nm FEL harmonics nm): 3 rd : 4.6 nm (270 eV) 5 rd : 2.7 nm (450 eV) Spectral width (FWHM): % Pulse energy: up to 50 µJ (average), 120 µJ (peak) Pulse duration (FWHM): fs Peak power (fundamental): Few GW Average power (fundamental): 0.1 W (up to 3000 pulses /sec) Photons per pulse: ~ FLASH: Key Performance Indicators Ackermann et al., Nature Photonics (2007)

FEL output builds up from spontaneous emission (photon noise) => SASE – ‘Self Amplified Spontaneous Emission’ O/P Profile and Spectral Distribution Spectral FluctuationsTemporal Fluctuations UXSS - SLAC. June 18, 2009

FEL output builds up from spontaneous emission (photon noise) => SASE – ‘Self Amplified Spontaneous Emission’ O/P Profile and Spectral Distribution Raw XUV Spectrum Corrected XUV Spectrum UXSS - SLAC. June 18, 2009

Part 2 - Experiments on dilute targets with FLASH Motivations 1. ‘FLASH’ Characterisation 2. Demonstration Experiments 3. Future (Path-finding) UXSS - SLAC. June 18, 2009

Atoms in Intense XUV + Optical (Ti-Sapphire - 800/400 nm) fields Photoionization of rare gas atoms dressed by intense optical fields Summary of Photoionization Experiments with the Ultrafast XUV Laser FLASH J T Costello, J Phys Conf Ser 88 Art No (2007) C. Bostedt et al., Experiments at FLASH, Nucl. Inst. Meth. in Res. A (2009 ) UXSS - SLAC. June 18, 2009

FLASH NIR/UV and XUV Beam Layout PG2 BL1 BL3 BL2 visible laser light UXSS - SLAC. June 18, 2009

E.S. Toma et al. PRA (2000) Two colour ATI/ Laser Assisted PES Electron Spectrometer Gas Jet NIR (800 nm) fs laser pulse XUV Superposition of visible and XUV pulses in a noble gas jet h  ir =1.55eV Ar(IP) eV Sideband intensity very sensitive to XUV- IR pulse area overlap. - Cross Correlation… Schins et al. PRL 73, 2180 (1994)

M Meyer et al., PRA (R) (2004) Cross (IR-XUV) correlation using HH XUV-IR Cross-Correlation H19 H17 (26eV) H21 Ar 3p 6 Ar + 3p 5 VUV IR e-e- 15,76 eV electron kinetic energy /eV Delay / fs Low field regime: Int(IR) ≈ W/cm 2  (sideband) 2 =  (IR) 2 +  (VUV) 2  T (laser) = 30fs

P. Radcliffe, et al., Nucl. Instr. and Meth. A 83, (2007) Two colour ATI/ Laser Assisted PES Experimental Layout at FLASH - (EU-RTD)

Two colour ATI/ Laser Assisted PES P. Radcliffe, et al., Nucl. Instr. and Meth. A 83, (2007) P. Radcliffe, et al., APL (2007) Sideband number/intensity depend strongly on XUV/NIR overlap  by comparison with theory we are able to determine relative time delay to better than 100 fs 550 fs 1. New ultrafast XUV-modulated optical-reflectivity methods 2. ‘TEO’ C. Gahl et al., Nature Photonics (2008) A. Azima et al., APL. T. Maltezopoulos et al., New J Phys 10 Art. No (2008) (2009)

A Maquet and R Taieb, J. Mod. Opt (2007) Two colour ATI - ‘Soft Photon’ - Classical excursion vector of an electron in a laser field of amplitude One photon cross-section ‘n’ photon ATI cross-section - Momentum transfer J n - Bessel function (first kind order ‘n’) After a little work………….sideband strength is given by an expression like…… k n - Shifted wavenumber of the ejected electron =  - Usual asymmetry parameter

Two colour ATI - Z Scaling 800 nm Ti-Sa 1.55 eV/ 120 fs FLASH h ~ 93 eV 20  J/pulse UXSS - SLAC. June 18, 2009 Low  Resonances   !

Two colour ATI - Z Scaling FEL Wavelength: 13.9 nm Fitted 800 nm intensity ~ 5 x W.cm -2 Intensity ratio of n = SB1/SB2( sidebands) - Model vs Experiment ‘Soft Photon’ Experiment UXSS - SLAC. June 18, 2009

2 colour ATI - FEL Wavelength Scaling FEL + LASER (800 nm) Sideband Ratios - Comparison of Soft Photon Approximation with Experiment UXSS - SLAC. June 18, 2009 where

2 colour ATI - Optical Intensity Scaling Ne: High dressing field sideband distribution UXSS - SLAC. June 18, 2009

2 colour ATI - Optical Intensity Scaling Ne: ‘Toy’ SFA Code / Asymmetry in sideband distribution Ne: Simulation h FEL = 46 eV UXSS - SLAC. June 18, 2009

FLASH: 13.7 nm, fs, 20µJ OL: 800nm, 4ps, 400µJ, 6 x W/cm 2 He 1s 2 + h XUV ----> He + 1s +  p He 1s 2 + h XUV + h OL ---> He + 1s +  s,  d  Atomic Dichroism in Two Colour ATI Strong Polarisation Dependence of Sidebands (Low Field) Meyer et al., PRL 101 Art. no (2008)

Atomic Dichroism in Two Colour ATI - He Low Optical Laser FieldHigh Optical Laser Field P. Theory: A Grum-Grzhimailo et al.SPA: A Maquet/ R Taieb Meyer et al., PRL 101 Art. no (2008)  (  ) = 3S d + (5S s + S d ) cos 2  S s /S d =1.25 ± 0.3

Atomic Dichroism in Inner-Shell ATI - Kr FLASH: 13.7 nm, fs, 20µJ OL: 800nm, 4ps, 6 x W/cm 2 SPA works well for both valence (4p) and inner shell (4s) electrons. UXSS - SLAC. June 18, 2009 Work in progress to determine  s /  d ratio from the above…..

Atomic Dichroism in Ionic ATI - Ne + Ne - Sequential Ionization ‘Work in progress’ - but we can begin to think about studying isonuclear trends……. UXSS, SLAC - June ‘Coherent’ blend of 3 P and 1 D sidebands…. ‘Isolated 3 P 1 st and 2 nd sidebands…. h FEL = 46 eV 1. Ne (2p 6 1 S) + h (46 eV)  Ne + (2p 5 2 P) + e - (~34 eV) 2. Ne + (2p 5 2 P) + h (46 eV)  Ne 2+ (2p 4 3 P/ 1 D) + e - (~ 2  5 eV)

UXSS, SLAC - June Atomic Dichroism in Ionic ATI - Ne + b =0.003 b =0.005 b =0.019 b =0.005 b =0.008 a + b Cos 2 (  ) SPA fits in progress… Core ‘ 2S+1 L J ’ effects ?

UXSS, SLAC - June Two Colour X-ray+NIR LSLS Collaboration: J. Bozek, A. Cavalieri, R. Coffee, J. Costello, S. Duesterer, R. Kienberger, M. Meyer, L. DiMauro & T. Tschentscher - LCLS, DESY, MPQ, DCU, Orsay & Ohio Experimental Plan for Fall 2009 and Proposed for 2010……. 1.Chirped Pulse Laser Assisted Auger Decay - CPLADD 2.Single Shot Atomic Streak Camera - SSASC Few Femtosecond Photo and Auger Electron Dynamics in Strong Optical Fields

Two Colour X-ray + NIR LSLS UXSS, SLAC - June Chirped Pulse Laser Assisted Auger Decay - CPLADD Target: Ne LCLS: eV ~50 fs Laser:800 nm or nm ~200 fs No Chirp 1. Auger electron: Linewidth independent of FEL BW (e.g., Ne eV) 2. Auger electron pulse mimics LCLS pulse: Electron replica  photocathode 3. No Chirp: Auger electron bunch exchanges photons with single carrier h L 4. Chirped: Auger bunch exchanges photons with time-varying carrier energy- Ergo different parts of the bunch experience different energy shifts - (time  energy) => sideband shape  X-ray pulse profile……… ChirpedChirped

Two Colour X-ray+NIR LSLS UXSS, SLAC - June Single Shot Atomic Streak Camera - SSASC Target: Rare gas, LCLS: >800 eV, ~1 - 4 fs, Laser: OPA (2000 nm, ~ 7 fs), 1. Electron bunch must replicate ultrashort X-ray pulse……. 2. Electron bunch duration must be shorter than one half cycle of the OPA dressing field (~ 3fs)…… 3. Photoelectron energy shift follows the electric field of the IR dressing laser….. 4. In the zero field crossing case the electron pulse is streaked in both directions resulting in a broadened but unshifted electron line - the electron linewidth will depend on the electron (X-ray) bunch length (case ‘b’) 5. On the other hand, if the electron bunch falls on the carrier peak, all parts of the bunch ‘feel’ approximately the same dressing field, ergo the electron bunch will be shifted by a constant energy (case ‘c’) 6. Postprocessing - retrieve zero crossing cases to determine LCLS pulse width distribution (< 1 to 4 fs ?) a. Without dressing field => unshifted, no broadening….. b. With dressing field (zero crossing) => unshifted, broadened….. c. With dressing field (peak value) => shifted, no broadening…..

Summary - Two Colour ATI 1.Demonstrated interference free SBs to high order, polarisation control, laser and FEL parameter dependencies & SBs in atomic and ionic targets 2.At low optical intensities 2nd order PT & SPA agree 3.Beyond He we really need to measure angular distributions to try to unravel the ‘l’ channels (Kr 4s ?) 4.SPA works well at high intensities but the number of open high angular momentum channels is a challenge for other approaches such as R-Matrix Floquet (HvdH) 5.Is there really value in going beyond SPA ? Does the residual ion core atomic structure really matter ? (Ne + ) 6.LCLS will test the limits of UF X-ray techniques…. UXSS, SLAC - June

Atoms in Intense XUV Fields UXSS, SLAC - June Part 3. Few XUV Photon Ionization

FLASH Offers………… UXSS, SLAC - June High intensity  J/10fs/10  m ~ W/cm 2 Expect few photon non-linear photoionization processes….. Interaction with matter High (XUV) photon energy eV Keldysh -  where

Atoms in Intense XUV Fields UXSS, SLAC - June Keldysh - Ionization Regime Multiphoton IonizationTunnel Ionization Field Ionization  >>1  ~ 2  <<1 Intensity/ Wavelength Photon Energy

UXSS, SLAC - June FLASH in the XUV - Pertubative (MPI) Regime: Ti-Sapphire in the NIR Non-Pertubative (TI) Regime So these non linear photoionization processes will involve predominantly few photons and potentially few electrons Keldysh - Ionization Regime Multiphoton IonizationTunnel Ionization Field Ionization  >>1  ~ 2  <<1

Xe ionization in intense XUV fields UXSS, SLAC - June Sorokin, Richter et al., PTB, PRL 2008

 4d h = 93 eV FEL only. h ~ 93 eV Xe + h  Xe + + e - Replace Ion TOF by MBES – photoelectron spectrosopy UXSS, SLAC - June Intensity scaling... Weakest field…

 4d two photon direct ionization FEL only. h ~ 93 eV Xe + 2h  Xe + + e - Must not ignore 4p- Auger processes also ! UXSS, SLAC - June Interpretation proving a challenge as ionization and excitation balance changes on a sub-fs timescale (and spatially)…….

Part 4. Next Steps Two Colour Resonant Photoionization Processes 1.To date we have looked only at one and two colour non-resonant processes 2. Next phase - FEL tunable and so we can explore resonant two colour processes where inner shell electrons dominate UXSS, SLAC - June

Kr 3d 10 4s 2 4p 6 Kr + 3d 9 2 D 5/2 4d XUV 46.1 eV Auger Kr + 4p 4 4d, 5d 92.0eV Experiment. June 15 (2009) MLM - 3 degree incidence……. Kr (3d 9 4d) 2 Photon Resonance Auger UXSS, SLAC - June Kr: 3d 10 4s 2 4p 6 + 2h (46 eV)  3d 9 4s 2 4p 6 4d  1. Kr + : 3d 10 4s 2 4p 4 4d +  l (~60 eV) 2. Kr + : 3d 10 4s 2 4p 5 +  l’ (~75 eV) Kr + 4p 5

Kr 3d 10 4s 2 4p 6 Kr + 3d 9 2 D 5/2 4d XUV 46.1 eV Auger Kr + 4p 4 4d, 5d 92.0eV Experiment. June 15 (2009) MLM - 3 degree incidence……. Kr (3d 9 4d) 2 Photon Resonance Auger UXSS, SLAC - June Kr + 4p 5 FLASH June 18, ca am CET Duesterer, Li & Richardson……

Upgrade at FLASH - Optical Parametric Amplifier - (fs OPA) Experiments post-upgrade Laser coupling/spectroscopy of autoionization states UXSS, SLAC - June

Bachau & Lambropoulos, PRA (1986) Themelis, Lambropoulos, Meyer, JPB (2005) ‘New Knobs’ 1.Laser Frequency 2.Laser Intensity Tunable Optical Laser - Laser Coupling of autoionization states - 'Autler Townes' Autoionizing Resonances - He Laser Coupled Autoionising State Dynamics UXSS, SLAC - June

FLASH - Technical Developments OPA Upgrade mJ/ ps Synchronisation - New FIR Undulator (THz) Seeding with HHs - Full coherence Stabilisation Synchroniosation UXSS, SLAC - June

In Conclusion 1.To date we have looked only at one and two colour non- resonant photoionization processes 2.Now - FEL easily tunable - we can explore resonant two colour processes where inner shell electrons dominate 3.Study fragmentation and ionization from vibrationally excited/selected wavepackets in simple molecules 4.Beyond 2009: FLASH - seeding, fs jitter, angle resolved PES,… X-rays - LCLS/XFEL/SPRING-8/NLS 5.The future is bright and the XUV & X-ray are even more exciting (now) (J-P Connerade, ICL) UXSS, SLAC - June