The Laser 50 Multiphoton Processes with EUV and

The Laser @ 50 Multiphoton Processes with EUV (and X-ray) Free Electron Lasers John T Costello National Centre for Plasma Science & Technology (NCPST)/ School of Physical Sciences, Dublin City University http: //www. ncpst. ie http: //www. physics. dcu. ie/~jtc Laser @ 50, QUB, September 13, 2010

Collaboration @ FLASH-DESY, Hamburg XFEL: P. Radcliffe & M. Meyer Paris (UPMC): R. Taieb (T) & A. Maquet (T) PTB (Berlin): A. A. Sorokin (now at IOFFE & DESY) & M. Richter DESY (Hamburg): K. Tiedke, S. Düsterer, W. Li, P. Juranić & J. Feldhaus Orsay: D. Cubaynes & D. Glijer Queen’s University Belfast: C. L. S. Lewis, A Delserieys, H. van der Hart (T) Moscow State University : A. N. Grum-Grzhimailo, E. V. Gryzlova, S. I. Strakhova Crete: P. Lambropoulos (T) Oulu/GSI: S. Fritzsche (T) DCU: V. Richardson, J. Dardis, P. Hayden, P. Hough, K. Kavanagh, T. J. Kelly, E. T. Kennedy, H. de Luna, J. P-Gutierrierz & J. T. Costello Thanks to AG Photon (R Treusch et al. ) & AG Machine (M Yurkov et al. ) � Laser @ 50, QUB, September 13, 2010

Collaboration @ FLASH-DESY, Hamburg Machine: Users: � Situation Normal ? Laser @ 50, QUB, September 13, 2010

Collaboration @ LCLS X-ray FEL (SLAC) MPQ/TU-Munich: A. Maier, W. Helml, W. Schweinberger & R. Kienberger SLAC: R. Coffee, J. Hastings & J. Bozek XFEL: P. Radcliffe, T. Tschenscher & M. Meyer DESY (FLASH): S. Düsterer & J. Feldhaus DESY (CFEL): I. Grguras & A. Cavalieri Ohio (OSU): C. Roedig, G. Doumy* & L. Di. Mauro DCU: T. J. Kelly, V. Richardson, L. Nikolopoulos (T) & J. T. Costello *Now at Argonne. � Laser @ 50, QUB, September 13, 2010

Collaboration @ LCLS X-ray FEL (SLAC) � Laser @ 50, QUB, September 13, 2010

DCU Laser Plasma/ AMOP Group 6 laboratory areas focussed on pulsed laser matter interactions (NIR – X-ray/ 30 fs – 30 ns, spectroscopy/ imaging/ PLD) Academic Faculty (5): John T. Costello, Eugene T. Kennedy (Emeritus), Jean-Paul Mosnier, Lampros Nikolopoulos (T) and Paul van Kampen Current Postdocs (3): Dr. Patrick Hayden, Dr. Sateesh Krishnamurthy and Dr. Subhash Singh Funded by: SFI - Frontiers and Investigator HEA – PRTLI (Kit) IRCSET (People) EU - Marie Curie (People) Current Ph. D students (9 + 1): Jack Connolly (JPM), Leanne Doughty (PVK), Brian Doohan (JC), Colm Fallon (JC), Eanna Mac Carthy (JPM), Mossy Kelly (JC), Vincent Richardson (JC), Jiang Xi (ETK/JC), Damien Middleton, (LN), open position (LN) Visiting Students: Ricarda Laasch (Univ. Hamburg) and Nadia Gambino (Univ. Catania) DCU International Visitng Fellow: Prof. Sivanandan Harilal (Purdu. E) Laser @ 50, QUB, September 13, 2010

Outline of Talk 1. FLASH FEL at DESY - Hamburg 2. USPs of XFELs in AMO Physics… 3. Setup for Photoelectron Spectroscopy @ FLASH 4. One Colour - 2 Photon Ionization Case Study 1: 2 -Photon 4 d-Ionization of Xe (ATI) Case Study 2: Resonant 2 -Photon 3 d-Excitation/Decay in Kr 5. Two Colour (Above Threshold) Ionization Case Study 1: Atomic dichroism in He (FLASH) Case Study 2: Ionization dynamics of atomic Ne (LCLS) 6. A Next Step: X-ray Coherent Control of Auger Decay 7. Some conclusions Laser @ 50, QUB, September 13, 2010

FLASH Overview 1. FLASH - Operation & Physical Layout RF-gun Diagnostics Accelerating Structures Bunch Compressor Laser 5 Me. V 127 Me. V Bunch Compressor 450 Me. V Collimator 1000 Me. V Undulators Bypass 300 m • LINAC Energy : ~ 1 Ge. V ~ 4 – 60 nm Laser @ 50, QUB, September 13, 2010 FEL Diagnostics

FLASH: Key Performance Indicators Wavelength range (fundamental): water window 4 - 60 nm (2010) FEL harmonics (@13. 7 nm): 3 rd : 4. 6 nm (270 e. V) 5 rd : 2. 7 nm (450 e. V) Spectral width (FWHM): 0. 5 -1 % Pulse energy: up to 50 µJ (average), 120 µJ (peak) Pulse duration (FWHM): 10 -20 fs Peak power (fundamental): Few GW Average power (fundamental): 0. 5 W (up to 10000 pulses /sec) Photons per pulse: ~ 1013 Nature Photonics 1 336 (2007)

O/P Profile and Spectral Distribution FEL output builds up from spontaneous emission (photon noise) => SASE – ‘Self Amplified Spontaneous Emission’ => Fluctuations in beam profile, pointing stability, intensity, spectral distribution and pulse duration !! Spatially coherent only - ‘Seeded FEL projects at FLASH & LCLS’ Spectral Fluctuations Temporal Fluctuations Nature Photonics 1 336 (2007)

(Currently) Operating EUV / X-ray SASE FEL Facilities Worldwide - Parameters 1. FLASH: 30 – 300 e. V/10 Hz (1 – 1000 micropulses/bunch) - 10 u. J/10 fs/micrpulse (CW RF) 2. LCLS (AMO): 1 n. C bunch: 0. 8 – 2 ke. V (60 Hz)/ 2. 5 m. J/250 fs 10 p. C bunch: 0. 8 – 2 ke. V (60 Hz)/50 u. J/ 1 – 4 fs 3. Spring-8 (SCSS): 20 - 22 e. V (60 Hz)/ 50 u. J/ 100 fs Laser @ 50, QUB, September 13, 2010

2. USPs of XFELs in AMOP ? • 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 NB 1: Makes inner-shell electrons key actors in non-linear processes for the first time NB 2: Re-asserts primacy of the photon over field effects ! Laser @ 50, QUB, September 13, 2010

Keldysh - Ionization Regimes Multiphoton Ionization >>1 Tunnel Ionization Field Ionization ~2 <<1 where Laser @ 50, QUB, September 13, 2010

Keldysh - Ionization Regime Multiphoton Ionization >>1 Tunnel Ionization Field Ionization ~2 <<1 For an irradiance: = 1015 W. cm-2 FLASH in the EUV (8 nm) - Ti-Sapphire in the NIR (800 nm) - ~ 45. 0 ~ 0. 45 Pertubative (MPI) Regime Non-Pertubative (TI) Regime So non linear photoionization processes at EUV & X-ray FELs will involve predominantly few photons and few electrons. … Note - ion yield scales with intensity as In Laser @ 50, QUB, September 13, 2010

EUV / XFEL AMO Physics Reviews 1. Photoionization Experiments with the Ultrafast XUV Laser FLASH J. T. Costello, J. Phys. Conf. Series 88 Art No. 012057 (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 601 pp 108 -122 (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 57 pp 1015 -1040 (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. 194006 (2010) Laser @ 50, QUB, September 13, 2010

3. Photoelectron Spectroscopy Setup Two colour ATI/ Laser Assisted PES Experimental Layout at FLASH - (EU-RTD) Nucl. Instr. and Meth. A 83, 516 -525 (2007)

Part 4. Two Photon Ionization (TPI) of atoms in an Intense Field Case 1. Non-Resonant: Xe @ h = 93 e. V Case 2. Resonant: Kr @ h = 46 e. V (3 d-4 d) Laser @ 50, QUB, September 13, 2010

Motivation - Xe TPI in intense EUV fields Sorokin, Richter et al. , PTB, PRL 2007 – Ion Spectroscopy !! Laser @ 50, QUB, September 13, 2010

Xe + h (93 e. V) - Xe+(4 d-1) + e- (~25 e. V) Electrons !!! • Single shot spectrum…. • For low intensities (<1013 W. cm-2), one photon processes are dominant • Salient features – spin orbit split 4 d photoelectron line + Auger electron spectrum • Not shown – 5 s-1 and 5 p-1 lines at higher KEs Laser @ 50, QUB, September 13, 2010

Xe + 2 h (93 e. V) - Xe+(4 d-1) + e- (~ 118 e. V) Now ramp up the intensity to > 1015 W. cm-2…………. • Using MBES, first evidence of two photon inner shell ionisation, (in this case) of 4 d electron – Xe + 2 hv → Xe+ 4 d 9 + e • ‘Retardation field’ applied to suppress low KE electrons (one photon processes) – hence electrons detected are due solely to multiphoton events • Energetically – 2 × (93) e. V – 118 e. V = 68 e. V • Yield scales quadratically, n=1. 95 ±. 2 Laser @ 50, QUB, September 13, 2010

1 to 2 Photon Ionization Branching Ratio 1. R-Matrix (H. W. Van der Hart) – one and two photon 4 d emission cross sections 2. Dominant process is one photon ionization – 93 e. V can remove next 4 d as well - or maybe excite 4 p – 4 d. High rate of ‘inside-out’ ionization……. 3. Accurate calculation requires a far more rigorous description of the atomic structure than at present 4. Estimated two photon 4 d-1 emission is ~1% of total at ~ 7 x 1015 W. cm-2 Laser @ 50, QUB, September 13, 2010

Read the full story here……. PRL 105 013001 2010

Case 2. Resonant 2 -photon Excitation (Kr) 1. To date we have looked at a non-resonant two photon process (sort of ATI really) 2. FELs are wavelength tunable - one can also explore resonant two photon processes Kr 3 d 104 s 24 p 6 (1 S 0) + 2 x h (46 e. V) -> 3 d 94 s 24 p 64 d (J=0, 2) 1. i. e. , 3 d - 4 d two photon resonant excitation Laser @ 50, QUB, September 13, 2010

Kr - Resonant Two Photon Excitation 1. Kr 3 d 104 s 24 p 6 (1 S 0) + 2 x h (46 e. V) -> 3 d 94 s 24 p 64 d (J=0, 2) i. e. , 3 d - 4 d two photon excitation h = 46 e. V (~27 nm) 2. Of course there is a direct ionization path and the usual interference results - manifested as asymmetric resonance profiles (Fano/ Fano-Mies) 3. But here the 3 d 94 s 24 p 64 d (J=0, 2) resonance undergoes Auger decay to Kr+ on a femtosecond timescale - similar to the FLASH pulse duration - so competition between excitation and decay (ergo, in addition to simple ATI, this case makes for an intriguing, problem for theory). . Meyer et al. , PRL 104 213001 (2010) Laser @ 50, QUB, September 13, 2010

94 d) 2 Photon Resonant Auger Kr (3 d Kr - Resonant Two Photon Excitation MBES Photoelectron spectrum - ~ 1014 W. cm-2 Auger ATI Laser @ 50, QUB, September 13, 2010

94 d) 2 Photon Resonant Auger Kr (3 d Kr - Resonant Two Photon Excitation MBES Photoelectron spectrum - ~ 1014 W. cm-2 Auger ATI Laser @ 50, QUB, September 13, 2010

94 d) 2 Photon Resonant Auger Kr (3 d Kr - Resonant Two Photon Excitation Ionization rates – P. Lambropoulos, Crete Laser @ 50, QUB, September 13, 2010

Read much more here……. Kr - Resonant Two Photon Excitation PRL 104 213001 (2010)

Summary - One Colour • Xenon - First detection of a so-called ‘above threshold ionization’ (ATI) two-photon process in an inner shell electron shell. • It is clear that the although single photon ionization processes dominate, they are sufficiently important at high irradiance that, for a given intensity, much higher ionization stages can be reached compared to optical lasers. • The strength and the nature of the 4 d → εf resonance may open up, at high irradiance, additional ionization channels, namely the simultaneous multiphoton / multi-electron from the inner 4 d shell, ‘inside-out ionization’ or ‘peeling the onion from the inside out’ • Kr - first step on the road to resonant NL processes with EUV/X-rays…. REMPI at X-ray. Xe - Richardson et al. PRL (July 2 – 2010), Kr - Meyer et al. , PRL (May 28 - 2010) Laser @ 50, QUB, September 13, 2010

Part 5. Atoms in Intense EUV (X-ray) + Optical (Ti-Sa - 800 nm) fields Case 1. (FLASH) Dichroism in He @ h FEL ~ 93 e. V Case 2. (LCLS - Preliminary) Atomic dynamics of Ne @ h FEL ~ 850 e. V Laser @ 50, QUB, September 13, 2010

FLASH NIR/UV and XUV Beam Layout PG 2 BL 1 BL 2 BL 3 800 nm, 120 fs Laser @ 50, QUB, September 13, 2010

Two colour ATI/ Laser Assisted PES Superposition of visible and XUV pulses in a noble gas jet Schins et al. PRL 73, 2180 (1994) Electron Spectrometer hwir =1. 55 e. V XUV NIR (800 nm) fs laser pulse Gas Jet Sideband intensity very sensitive to XUV- Ar(IP) IR pulse area overlap. - Cross Correlation… E. S. Toma et al. PRA 62 061801 (2000) 15. 76 e. V

Two colour ATI/ Laser Assisted PES FLASH: 13. 7 nm, 10 -30 fs, 20µJ Optical Laser: 800 nm, 120 fs, 400µJ, 5 x 1013 W/cm 2 He 1 s 2 + h XUV ----> He+ 1 s + p He 1 s 2 + h XUV + nh OL ---> He+ 1 s + s, d Laser @ 50, QUB, September 13, 2010

Two colour ATI/ Laser Assisted PES 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 2 165 -169 (2008) A. Azima et al. , APL, T. Maltezopoulos et al. , New J Phys 10 Art. No. 033026 (2008) 94 144102 (2009) Nucl. Instr. and Meth. A 83, 516 -525 (2007) Appl. Phys. Lett 90 131108 (2007)

Atomic Dichroism in Two Colour ATI - He Strong Polarisation Dependence of Sidebands (Low Field) FLASH: 13. 7 nm, 10 -20 fs, 20µJ OL: 800 nm, 4 ps, 400µJ, 6 x 1011 W/cm 2 He 1 s 2 + h XUV ----> He+ 1 s + p He 1 s 2 + h XUV + h OL ---> He+ 1 s + s, d PRL 101 Art. no. 193002 (2008)

Atomic Dichroism in Two Colour ATI - He Low Optical Laser Field High Optical Laser Field ( ) = 3 Sd + (5 Ss + Sd) cos 2 Ss/Sd =1. 25 ± 0. 3 P. Theory: A Grum-Grzhimailo et al. SPA: A Maquet/ R Taieb PRL 101 Art. no. 193002 (2008)

Two Colour X-ray + NIR Expts @ LCLS Collaboration: R. Kienberger, J. Bozek, A. Cavalieri, R. Coffee, J. Costello, S. Duesterer, M. Meyer, L. Di. Mauro & T. Tschentscher - MPQ, LCLS, DESY, DCU, DESY, XFEL & Ohio State Few Femtosecond Photo and Auger Electron Dynamics in Strong Optical Fields Idea. LCLS has a ‘low bunch current mode’ which allows it to deliver ultrashort pulses of duration: 1 - 4 fs…. . So we are using the Single Shot Atomic Streak Camera or SSASC technique* to measure it. * R. Kienberger et al. , J. Mod. Opt 52 261 -275 (2005) Laser @ 50, QUB, September 13, 2010

Two Colour X-ray + NIR Expts @ LCLS Single Shot Atomic Streak Camera – SSASC => few fs pulse widths Target: Neon, LCLS: >850 e. V, ~1 - 4 fs, Laser: OPA (2000 nm, ~ 7 fs), a. Without dressing field => unshifted, no broadening…. . b. With dressing field (zero crossing) => unshifted, broadened…. . c. With dressing field (peak value) => shifted, not broadened…. . 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 (~ 3 fs)…… 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 ? ) Laser @ 50, QUB, September 13, 2010

Two Colour X-ray + NIR Expts @ LCLS First test experiment at LCLS - sideband generation. Target: Ne November 2009 Test Data LCLS: 840 - 850 e. V ~50 -250 fs SSASC data from July 2010 under analysis Laser: 800 nm/ ~1 m. J ~35 fs Laser @ 50, QUB, September 13, 2010

Summary - Two Colour ATI 1. So far we have demonstrated interference free SBs to high order, polarisation control, laser and FEL parameter dependencies & SBs in atomic/ionic targets 2. At low optical intensities 2 nd order PT & 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 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 pulse/jitter measurement techniques – ‘Tandem streaking’ experiment under review for beamtime……… Laser @ 50, QUB, September 13, 2010

6. Next step: X-ray coherent control ? Resonant ATI or RATI Neon: (Very) Simplified Energy Level Scheme AIS Ne - 1 s-13 p(1 P 1) Auger Emission Rabi-Flopping Ne+ - 2 p 5(2 P 1/2, 3/2) Ne - 2 p 6(1 S 0) GS Laser @ 50, QUB, September 13, 2010

Next steps: X-ray coherent control ? Another proposed scheme: Bozek (SLAC), Cavalieri (CFEL), Coffee (SLAC), Costello (DCU), Di Mauro (OSU), Duesterer (DESY-FLASH), Hastings (SLAC), Kelly (DCU), Kennedy (DCU), Kienberger (MPQ/TUM), Nikolopoulos (DCU – Theory) Meyer (XFEL), Radcliffe (XFEL) and Tschenscher (XFEL) Laser @ 50, QUB, September 13, 2010

Ne Auger Splitting for 908 e. V Pump Ne + h (908 e. V) -> Ne+ (k-1) + e- -> Ne 2+ (2 p 4) + h (pump, 908 e. V) Irradiance @ 908 e. V: 3. 5 x 1016 W. cm-2 Calculation – Lampros Nikolopoulos (DCU) Laser @ 50, QUB, September 13, 2010

Ne Fluor Splitting for 891 e. V Pump Ne+ (1 s-13 p) -> Ne+ (2 p 5 2 P 3/2, 1/2) Irradiance @ 891 e. V: 3. 5 x 1016 W. cm-2 Calculation – Lampros Nikolopoulos Laser @ 50, QUB, September 13, 2010

So what’s really new/ different about NL • Importantly - EUV/X-ray FELs bring inner shell electrons into the non. Optics/ Spec with X-ray Lasers ? linear interaction of radiation with matter for the first time…. . ’inside out ionization’…. . • So Auger states (with femtosecond lifetimes) can play a key role in the process…. This will lead to a complex dynamical interaction between the EUV/X-ray excitation and decay which means that simple ‘Single Active Electron - SAE’ models will no longer suffice…. . … • Self-consistent atomic structure and dynamics models that can combine and capture the physical competition between pumping and rapid (mainly) non-radiative decay of small quantum systems, along with a gamut of other parasitic/competitive non-linear (e. g. , ATI) and correlative processes (e. g. , shake up/down) in intense EUV/X-ray fields are now needed for matter from atoms to macromolecular systems……. Laser @ 50, QUB, September 13, 2010

What invest in AMOP at XFELs ? “FELs operating at wavelengths comparable to the atomic unit of space and with pulse durations which will approach the atomic unit of time will permit the atomic nature of systems ranging from complex rogue macromolecules to nanostructures to be distinguished, extracted and possibly even controlled. All such future studies will rely on a continuing stream of innovative, critically executed and evaluated FLASH to XFEL photoionization experiments on simple prototypical atomic and molecular systems. ” Laser @ 50, QUB, September 13, 2010

In Summary Conclusion To date: We have looked only at one and two colour non-linear photoionization processes in atoms Also we have explored one example and can explore many more resonant multiphoton processes where inner shell electrons dominate Next: Extend two colour pump-probe experiments to atomic ions & fragmentation/ ionization from vibrationally excited/selected wavepackets in molecules 2011 and beyond: FLASH & SCSS - seeding, fs jitter, angle resolved PES, …… LCLS/XFEL - few fs pulses, ‘spoilers’ for cleaner pulses, seeding (Echo 7 project), etc…… “The VUV is more exciting” (J-P Connerade, IC London) Laser @ 50, QUB, September 13, 2010

Why TPI in Atomic Xe only ? 1. However, from Sorokin et al. PRL 99 (2007) 213002 one may conclude that the FEL field produces and interacts with a highly ionized target. 2. Xe+ has four 4 d-1 ionization thresholds at 71. 6 e. V, 72. 9 e. V, 74. 9 e. V, and 76. 2 e. V - yield photolines with KE from 110 to 115 e. V. However, Xe+ appears only weakly in the ion spectra even at very high FEL intensity. 3. 4 d-1 from higher charge states also possible – outside KE region of interest 4. Additionally, two photon O-shell ionisation cross section are weak at 93 e. V for XE ions, even for Xe 4+ & Xe 5 with nearby resonances: J-M. Bizau et al………. . Laser @ 50, QUB, September 13, 2010