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 EUV and Optical Fields at FLASH Ultrafast Imaging Workshop, Ischia May 3, 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 Ultrafast Imaging Workshop, Ischia May 3, 2009

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 Ultrafast Imaging Workshop, Ischia May 3, 2009

FLASH (Brief) Overview Atoms & Molecules in Intense EUV + NIR Fields Coherent Photoionization Processes in Superposed Fields Optically probing fragments in EUV dissociated H 2 Two Photon Ionization in Intense EUV Fields Next steps Outline of the Talk Ultrafast Imaging Workshop, Ischia May 3, 2009

Part 1 - FLASH Overview Ultrafast Imaging Workshop, Ischia May 3, 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 Ultrafast Imaging Workshop, Ischia May 3, 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 70 µJ (average), 170 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 Ultrafast Imaging Workshop, Ischia May 3, 2009

FEL output builds up from spontaneous emission (photon noise) => SASE – ‘Self Amplified Spontaneous Emission’ O/P Profile and Spectral Distribution Raw EUV Spectrum Corrected EUV Spectrum Ultrafast Imaging Workshop, Ischia May 3, 2009

Part 2 - Experiments on dilute targets with FLASH Motivations 1. ‘FLASH’ Characterisation 2. Demonstration Experiments 3. Future (Pathfinding) Ultrafast Imaging Workshop, Ischia May 3, 2009

Atoms & Molecules in Intense EUV + Optical (800/400 nm) fields 1.Photoionization of rare gas atoms dressed by intense optical fields 2.Optical probing EUV dissociated H 2 Summary of Photoionization Experiments with the Ultrafast EUV Laser FLASH - Free Electron Laser in Hamburg 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) Ultrafast Imaging Workshop, Ischia May 3, 2009

FLASH NIR/Vis and EUV Beam Layout PG2 BL1 BL3 BL2 visible laser light Ultrafast Imaging Workshop, Ischia May 3, 2009

E.S. Toma et al. PRA (2000) Two colour ATI/ Laser Assisted PES Electron Spectrometer gas jet Visible fs laser pulse VUV Superposition of visible and VUV pulses in a noble gas jet Ar(IP) eV h  ir =1.55eV Sideband intensity very Sensitive to overlap Schins et al. PRL 73, 2180 (1994)

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 EUV/NIR overlap  by comparison with theory we are able to determine relative time delay to better than 100 fs 550 fs 1. New ultrafast EUV-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) (In Press 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

Two colour ATI - Z Scaling Fitted 800 nm intensity ~ 5 x W.cm -2 Ultrafast Imaging Workshop, Ischia May 3, 2009 Intesnity ratio of n= 1:2 sidebands - Model vs Experiment ‘Soft Photon’ Experiment

2 colour ATI - FEL Wavelength Scaling FEL nm. SB Ratio - Comparison of SPA with Experiment Ultrafast Imaging Workshop, Ischia May 3, 2009

2 colour ATI - Optical Intensity Scaling Ultrafast Imaging Workshop, Ischia May 3, 2009 Ne: Asymmetry in sideband distribution

Ultrafast Imaging Workshop, Ischia May 3, colour ATI - Optical Intensity Scaling Ultrafast Imaging Workshop, Ischia May 3, 2009 Ne: ‘Toy’ SFA Code / Asymmetry in sideband distribution Ne: Simulation h FEL = 46 eV

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 Two colour ATI - Kr FLASH: 13.7 nm, fs, 20µJ OL: 800nm, 4ps, 6 x W/cm 2 Ultrafast Imaging Workshop, Ischia May 3, 2009 AD in TC-ATI: Ne, Kr, Xe: work in progress

Atomic Dichroism in 2 colour ATI - Ne + Ultrafast Imaging Workshop, Ischia May 3, 2009 Sequential Ionization ‘Work in progress’ - but we can begin to think about studying isonuclear trends…….

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 OPT & SPA agree 3.Beyond He we really need to measure angular distributions to try to unravel the ‘l’ channels… 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 here ? Does the residual ion core atomic structure really matter….? Ultrafast Imaging Workshop, Ischia May 3, 2009

Demonstration Experiment Optical Probing of H 2 Dissociation

< 100 fs h VUV H(1s) + H(1s) H + + H(1s) H + + H(nl) H + + H + FEL : 13.7 nm, 90.5 eV 1) H 2 + h (FEL) --> H + H* Opt.Las. : 400 nm, 3.1 eV 2) H* + h (las) --> H + + e - Optical Probing of H 2 Dissociation Ultrafast Imaging Workshop, Ischia May 3, 2009

Optical Probing of H 2 Dissociation 13.7 nm (pump) nm (probe) Low Intensity (0.5 mJ/120 fs) High Intensity (1.5 mJ/120 fs)

Ultrafast Imaging Workshop, Ischia May 3, 2009 Dynamics - more to do - jitter limited. Optical Probing of H 2 Dissociation expt. fit risetime = 500 fs

Ultrafast Imaging Workshop, Ischia May 3, 2009 Xe ionization in intense EUV fields

Ultrafast Imaging Workshop, Ischia May 3, 2009  4d two photon direct ionization FEL only. h ~ 93 eVXe + 2h  Xe + + e - Replace PIS by MBES - First evidence of inner-shell TPI

Part 3. Current and Future Interests 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 Ultrafast Imaging Workshop, Ischia May 3, 2009

Kr 3d 10 4s 2 4p 6 Kr + 3d 9 2 D 5/2 4d VUV 46.1 eV Auger Kr + 4p 4 4d, 5d ? 92.0eV Expt. June 2009 (Hopefully) MLM - 3 degree incidence Kr (3d 9 4d) 2 Photon Resonance Auger

First Effort: Resonant Auger Spectrum TOF (ns) 4p 4s SB FEL+las FEL Kr (3d 9 4d) DOR-Auger Next Expt: h FEL (89 eV) + h OL (3.1 eV) Ultrafast Imaging Workshop, Ischia May 3, 2009 Kr 3d 10 4s 2 4p 6 Kr + 3d 9 2 D 5/2 4d 5p XUV 13.9 nm Auger Kr + 4p 4 4d, 5d ? 92.0eV 1.55 eV

Upgrade - Optical Parametric Amplifier - (fs OPA) Experiments post-upgrade Laser coupling/spectroscopy of autoionization states - 'Autler-Townes' meets ‘Codling-Madden’ Ultrafast Imaging Workshop, Ischia May 3, 2009

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 Ultrafast Imaging Workshop, Ischia May 3, 2009

FLASH - Technical Developments OPA Upgrade mJ/ ps Synchronisation - New FIR Undulator (THz) Seeding with HHs - Full coherence Stabilisation Synchroniosation Ultrafast Imaging Workshop, Ischia May 3, 2009

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: Seeding, fs jitter, angle resolved PES,… 5. LCLS/XFEL/SPRING-8/NLS……….. Ultrafast Imaging Workshop, Ischia May 3, 2009