Intense EUV and X-ray Free Electron Laser Interactions with Atomic Beams. John T. Costello

Transcription

1 Intense EUV and X-ray Free Electron Laser Interactions with Atomic Beams John T. Costello National Centre for Plasma Science & Technology (NCPST)/ School of Physical Sciences, Dublin City University

2 What happens to atoms in ultraintense, femtosecond extreme-uv and X-ray free electron laser fields? John T. Costello National Centre for Plasma Science & Technology (NCPST)/ School of Physical Sciences, Dublin City University

3 Outline of the Talk Part I - How does an X-ray FEL work the SASE process? Part II Atoms in high intensity X-ray fields and the Keldysh factor essential physics with just one parameter. Part III Some non-linear EUV (optical) processes Two photon ionization Streaking spectroscopy Atomic Streak Camera Part IV Some perspectives

4 DCU Laser Plasmas / Atomic Physics Laser NCPST - 6 laboratory areas focussed on pulsed laser matter interactions (spectroscopy/ imaging) Academic Faculty (5): John T. Costello, Eugene T. Kennedy, Jean-Paul Mosnier, Paul van Kampen & Lampros Nikolopoulos (T) Current Postdocs (1): Dr. Colm Fallon and Dr. Mossy Kelly Current PhD students (10): D Middleton, Cathal O Broin, Nichola Walsh, Brian Sheehy, Ben Delaney, Stephen Davitt, Lu Hu, Getasew Admasu, William Hanks, Paul Grimes Recent Nat l / Int l Interns: Ricarda Laasch (Univ. Hamburg), Nadia Gambino (Univ. Catania, Sicily), Julien Witz (Ecole Polytechnique, Palaiseau, Paris Sud), K. Nishant. R. Tejaswi, (LNMIIT, Jaipur), Conor Hand, (NUIM) Recent Grads ( ): Padraig Hough, Conor McLoughlin, Rick O Haire, Vincent Richardson, Dave Smith, Tommy Walsh, Jack Connolly, Brian Doohan, Jiang Xi, Leanne Doughty, Eanna MacCarthy, Colm Fallon, Mossy Kelly Recent Postdocs ( ): Satheesh Krishnamurthy (OU UK), Pat Yeates (Elekta Oncology UK), Subhash Singh (U. Allahabad), Paddy Hayden (UCD)

5 DCU Laser Plasmas / Atomic Physics Laser NCPST - 6 laboratory areas focussed on pulsed laser matter interactions (spectroscopy/ imaging) Research Domains: 1. Colliding Laser Produced Plasmas 2. Optical and Particle Diagnostics of Laser Produced Plasmas 3. Laser Induced Breakdown Spectroscopy (LIBS) in the Vacuum-UV 4. Pulsed Laser Deposition (PLD) of Materials 5. Photoionization of Atoms and Ions with Laser Plasma and Free Electron Laser Light Sources Some Current Projects: 1. UV-Vis imaging, spectroscopy and interferometry of colliding laser produced plasmas [with and without laser reheating] 2. Double Pulse VUV-LIBS for Elemental Characterisation in Steel 3. Ion emission from single and colliding laser plasmas 4. PLD and in-situ P-type doping of ZnO nanostructures 5. 2 photon and 2 colour photoionization of atoms with EUV FEL

6 Part I. 1. X-ray How to Free achieve Electron X-ray Lasers lasing (FEL) 1. Try to create a population inversion between the well spaced energy levels in highly charged ions Optically pumped, collisional and recombination lasers expensive and difficult (Livermore, Osaka, Princeton PPL, NRL, Rutherford, etc.). 2. Frequency up-conversion by generating high harmonics of an optical laser (low fluxes, hard to scale to X-rays but can yield sub-100 as pulses!!!) 3. Make free electron lasers by injecting low emittance electron bunches, supplied by high energy (GeV) linear accelerators into periodic magnetic structures.

7 Part I. X-ray Free Electron Lasers (FEL) The Holy Grail is an X-ray laser with variable pulse duration on the femtosecond to attosecond timescales, tunable wavelength and high energy per pulse (few 100 µj to few mj) realised as the SASE EUN and X-ray FELs at SLAC-Stanford, SCSS & SACLA-RIKEN, FLASH-DESY (future European XFEL), FERMI-Trieste, SwissFEL-PSI,.. Very recently [2012] seeding of LCLS, SCSS and FERMI have resulted in transform limited pulses with Δλ/λ values of ~ 10-4

8 Part I. X-ray Free Electron Lasers (FEL) Spectral Range: IR to the X-ray Graphic: Courtesy, Prof. David Attwood (Berkeley)

9 Part I. X-ray Free Electron Lasers (FEL) Main Components of an X-ray FEL

10 FLASH Overview Part I. X-ray Free Electron Lasers (FEL) RF-gun" Diagnostics" Accelerating Structures" Collimator" Undulators" Laser" Bunch Compressor" Bunch Compressor" 5 MeV" 127 MeV" 450 MeV" 1000 MeV" 300 m" LINAC Energy : ~ 1 GeV ~ 4 60 nm FLASH - Operation & Physical Layout Bypass" FEL Diagnostics"

11 FLASH NIR/UV and XUV Beam Layout BL1 PG2 BL2 BL3 visible laser light

12 FLASH: Key Performance Indicators Wavelength range (fundamental): water window 4-60 nm (2010) 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): 0.5 W (up to pulses /sec) Photons per pulse: ~ Nature Photonics (2007)

13 Part II. Atoms in Intense X-ray Fields The Atomic (Einstein) Photoelectric Effect a) Single Photon Ionization (SPI) b) Multi Photon Ionization (MPI) KE(e - ) = hν EUV - IP KE(e - ) = nhν NIR - IP e - IP (EUV Synchrotron) IP (NIR Laser)

14 Part II. Atoms in Intense X-ray Fields What happens as the laser intensity (field strength) grows? Intensity/ Wavelength Photon Energy

15 Part II. Atoms in Intense X-ray Fields How can you determine in which regime the interaction resides? γ = IP 2U p Keldysh Parameter IP = Ionization Potential Up = Ponderomotive Pot. U = I( Wcm 2 ) λ 2 ( µm) ev P *L V Keldysh, Sov.Phys-JETP (1965)"

16 Keldysh - Ionization Regime Multiphoton Ionization Tunnel Ionization Field Ionization γ>>1 γ ~ 2 γ <<1 Intensity/ Wavelength Photon Energy

17 Keldysh - Ionization Regime Multiphoton Ionization Tunnel Ionization Field Ionization γ>>1 γ ~ 2 γ <<1 Example: Helium in intense laser fields For Ti-sapphire laser: 800 nm, Wcm -2, γ ~0.45 (TI/FI regime) For an EUV laser: 8 nm, Wcm -2, γ ~45 (MPI regime) U = I( Wcm 2 ) λ 2 ( µm) ev P So for EUV and X-ray lasers, multi-photon ionization is the primary processs and will involve few photons and potentially few electrons

18 Part II. Atoms in Intense X-ray Fields USPs of XUV & XFELs in AMO Physics? Ultra-dilute targets Photo-processes with ultralow cross-sections Pump and probe experiments (EUV + EUV or EUV + Opt.) Single shot measurements Few-photon single and multiple ionization processes NB1: Makes inner-shell electrons key actors in non-linear processes for the first time NB2: Re-asserts primacy of the photon over field effects!

19 Part II. Atoms in Intense X-ray Fields DCU: T. Kelly, N. Walsh, E. Kennedy, V. Richardson, J. Dardis, P. Hayden, P. Hough, H. de Luna, K. Kavanagh, J. P-Gutierrierz, L. Nikolopoulos (T) & J. T. Costello XFEL: T. Mazza, P. Radcliffe, T. Tschenscher & M. Meyer DESY (FLASH): K. Tiedke, S. Düsterer, W. Li, P. Juranić & J. Feldhaus DESY (CFEL): I. Grguras, M Hoffmann & A. Cavalieri MPQ/TU-Munich: A. Maier, W. Helml, W. Schweinberger & R. Kienberger Moscow State: N. Kabachnik, A. N. Grum-Grzhimailo, E. V. Gryzlova, S. I. Strakhova Crete: P. Lambropoulos (T) Ohio State (OSU): C. Roedig, G. Doumy* & L. DiMauro (*Now at Argonne) GSI: S. Fritzsche (T) (Now at Jena) PTB (Berlin): A. A. Sorokin (now at IOFFE & DESY) & M. Richter SLAC: R. Coffee, S Schorb, J. Hastings & J. Bozek Tohuku University (Sendai): K. Ueda QUB (Belfast): C. L. S. Lewis, A Delserieys, H. van der Hart (T)

20 Part II. Atoms in Intense X-ray Fields 1. Photoionization Experiments with the Ultrafast XUV Laser FLASH J. T. Costello, J. Phys. Conf. Series 88 Art No (2007) 2. Experiments at FLASH C. Bostedt, H. N. Chapman, J. T. Costello, J. R. Crespo Lopez-Urrutia, S. Duesterer, S. W. Epp, J. Feldhaus, A. Foehlisch, M. Meyer, T. Mšller, R. Moshammer, M. Richter, K. Sokolowski-Tinten, A. Sorokin, K. Tiedtke, J. Ullrich and W. Wurth, Nucl. Inst. Meth. in Res. A (2009) 3. Non-linear processes in the interaction of atoms and molecules with intense EUV and X-ray fields from SASE free electron lasers (FELs) N. Berrah, J. Bozek, J. T. Costello, S. Duesterer, L. Fang, J. Feldhaus, H. Fukuzawa, M. Hoener, Y. H. Jiang, P. Johnsson, E. T. Kennedy, M. Meyer, R. Moshammer, P. Radcliffe, M. Richter, A. Rouzee, A. Rudenko, A. Sorokin, K. Tiedtke, K. Ueda, J. Ullrich and M. J. J. Vrakking, Journal of Modern Optics (2010) 4. Two-colour experiments in the gas phase M. Meyer, J. T. Costello, S. Düsterer, W. B. Li and P. Radcliffe J. Phys. B: At. Mol. Opt. Phys. 43 Art No (2010)

21 Part II. Atoms in Intense X-ray Fields 1. Spectroscopic characterization of vacuum ultraviolet free electron laser pulses, Optics Letters (2006) 2. Two-color photoionization in xuv free-electron and visible laser fields, Phys. Rev. A 74, Rapid Communications, Art. no (2006) 3. Single-shot characterization of independent femtosecond extreme ultraviolet free electron and infrared laser pulses, Appl. Phys. Lett 90, Art. no (2007) 4. Operation of the Free Electron Laser FLASH in the water window, Nature Photonics (2007) 5. An experiment for two-color photoionization using high intensity extreme-uv free electron and near-ir laser pulses, Nucl. Inst. Methods in Res. A 583 pp (2007) 6. Polarization control in atomic 2-color above threshold ionization, Phys. Rev. Letts 101 Art. no (2008) 7. Time-resolved pump-probe experiments beyond the jitter limitations at FLASH, Appl. Phys. Letts 94 Art. no (2009) 8. Two-Photon Excitation and Relaxation of the 3d-4d Resonance in Atomic Kr, Phys. Rev. Letts 104 Art. no (2010) 9. Two-photon inner-shell ionization in the extreme-ultraviolet (XUV), Phys. Rev. Letts 105 Art. no (2010) 10. Two-color experiments in the gas phase at FLASH, J. Electron. Spec. Relat. Phenom. 181 pp (2010) 11. Femtosecond x-ray pulse length characterization at the LCLS FEL, New J. Phys. 13 Art. no (2011) 12. Theory of ac-stark splitting in core-resonant Auger decay in strong x-ray fields, Phys. Rev. A 84 Art. no (2011) 13. Angle-resolved electron spectroscopy of laser-assisted Auger decay induced by a few-fs x-ray pulse, Phys. Rev. Letts. 108 Art. no (2012) 14. Atomic photoionization in combined intense XUV free-electron and infrared laser fields, New J. Phys (2012) 15. Dichroism in the above-threshold two-colour photoionization of singly charged neon, J. Phys. B: At. Mol. Opt. Phys (2012) 16. Controlling core hole relaxation dynamics via intense optical fields, J. Phys. B: At. Mol. Opt. Phys (2012) 17. Ultrafast X-ray pulse temporal characterization for free-electron lasers, Nature Photonics (2012)

22 Part III. Non-linear processes in the X-ray Question. What is the simplest experiment you can carry out in non-linear optics? Answer. Either two-photon absorption (TPA) or second harmonic generation (SHG).. P.A. Franken et al, PRL 7, 118 (1961) From talk by Margaret Murnane, JILA, Colorado, a pioneer in HHG and co-founder of KM Labs, a manufacturer of ultrafast femtosecond laser systems Laser field! Ruby laser! Lens! Nonlinear electron motion! E P (!)=E 0 i!t! Quartz crystal! t! d(!)=a 1 ei!t + a 2 e i2!t +! Prism! 347nm! 694nm Photographic plate!! +! = 2!"

23 Part III. Non-linear processes in the X-ray Question. What is the simplest experiment you can carry out in non-linear optics? Answer. Either two-photon absorption (TPA) or second harmonic generation (SHG) nm 420 nm 694 nm 1 2

24 Part III. Non-linear processes in the X-ray To date ALL two photon absorption experiments have involved excitation of a valence electron only, i.e., bound electronic states With an X-ray FEL we should be able to excite (ionize) inner shell electrons It would be really interesting to see if we could get one of those electrons to absorb two photons because physics tell us that that is really hard to do at X-ray wavelengths

25 Part III. Non-linear processes in the X-ray First two-photon absorption experiment on inner shell electron ionization: Xe + 2hν (93 ev) -> Xe + + e - (118 ev) High quality, Si/Mo multilayer mirror employed spot size at focus ~ 4µm Wcm -2 (IOF-Jena) hν = 93 ev (13.5 nm EUVL Wavelength) Gas Monitor Detector (GMD) provides shot-toshot measure of FEL pulse intensity 0.65m Electron TOF - spectrometer - shaped magnetic field to maximise collection efficiency

26 Part III. Non-linear processes in the X-ray 1. First evidence of two photon inner shell ionisation, (in this case) of 4d electron Xe + 2hv Xe + 4d 9 + e - 2. Retardation field applied to suppress low KE electrons (one photon processes) hence electrons detected are due solely to multiphoton events 3. Energetically 2 (93) ev 118 ev = 68 ev 4. Yield scales quadratically, n=1.95 ±.2

27 More details here. PRL 105 Art. No (2010)

28 Kr - Resonant Two TPI of Photon Kr, 3d Excitation 4d hν = 46 ev (~27 nm) MBES Photoelectron spectrum φ ~ 5 x W.cm -2 PRL 104 Art. No (2010)

29 Part III. Two-photon ionization Future application?: Two photon imaging of molecules with chemical sensitivity provided by electron spectroscopy. Two-photon optical imaging well established in biomolecular physics.

30 Part IV. Streaking Spectroscopy Two colour photoionization experiments The Atomic X-ray Streak Camera The key diagnostic in ultrafast laser and optical physics is the Streak Camera. It is essentially an optical oscilloscope where the input channel is a photocathode as opposed to the usual direct electrical BNC input.. Hamamatsu Synchroscan Camera

31 Part IV. Streaking Spectroscopy Streak Camera Operation Courtesy Hamamatsu Corp. V(t) t

32 Part IV. Streaking Spectroscopy The Streak camera essentially maps time on a typically picosecond scale onto space on a mm scale, t -> x.

33 Atomic (Photoelectron) Streak Cameras a. Without dressing field => unshifted, no broadening.. b. With dressing field (zero crossing) => unshifted, broadened.. c. With dressing field (peak value) => shifted, not broadened.. Single Shot Atomic Streak Camera SSASC => few fs pulse widths. Target: Neon, LCLS: >870 ev, ~1-4 fs Laser: OPA (2000 nm, ~ 7 fs)

34 Single Cycle THz FLASH 34 Femtosecond Atomic Streak Camera Generate single (picosecond) cycle pulse using optical rectification of Ti-Sappire laser pulses field ~ 50MV/m maximum Schematic layout of the THz Streaking Experiment at FLASH Nature Photonics 6 pp (2012)

35 Single Cycle THz FLASH 35 Femtosecond Atomic Streak Camera Generate single (picosecond) cycle pulse using optical rectification of Ti-Sappire laser pulses field ~ 50MV/m maximum Principle of the experiment Attosecond Photoelectron Streaking showing how the E- field of a few cycle fs laser pulse can be mapped MPI-Q.

36 Single Cycle THz Streaking 36 A Cavalieri et al. from CFEL, DCU, XFEL & DESY Single cycle THz Photoelectron Streaking showing how the E- field of a single cycle ps laser pulse can be mapped Jitter measurements on 50 consecutive streak traces Nature Photonics 6 pp (2012)

37 XFEL Driver - imaging single molecules! Single shot dynamic coherent diffraction imaging on femtosecond timescales - soon to be used in single biomolecular imaging to make molecular movies!!! Cf: CFEL, DESY and PULSE, Stanford

38 X-Ray Lasers - Future What is hugely significant and exciting about X-ray FELs is that they operate at wavelengths comparable to the atomic unit of space and with pulse durations which are approaching the atomic unit of time. Hence the atomic nature of systems ranging from complex rogue macromolecules to nanostructures may be distinguished, extracted and possibly even controlled, at unprecedented space and time resolution, especially in key moieties, for the very first time.

39 Support Higher Education Authority Programme for Research in Third Level Institutes (IV and V) Science Foundation Ireland Investigator Programmes 07/IN.1/I1771 & 12/IA/1742 Irish Research Council (PhD Scholarships / Postdoctoral Fellowships) EU FP7 Erasmus Mundus Joint Doctorate EXTATIC EUV and X-ray Technology and Training for Interdisciplinary Cooperation Grant No. FPA

40 Colliding Plasmas-Spectroscopy ICCD Spectroscopy: Time and space resolved.

41 Double Pulse TI-SR VUV Space Resolving Geometry

42 X-Ray In Conclusion Lasers - Future 1. To date we have looked only at one and two colour nonresonant 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. Next steps: X-CPA Seeded FELs XFELs are finally becoming real lasers truly monochromatic, fully phase coherent, collimated... If it can be done with an optical laser now propose it for XFELs.