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Stimulated electronic x-ray Raman scattering at XFELs

Stimulated electronic x-ray Raman scattering at XFELs. Nina Rohringer Max Planck Institut für Physik Komplexer Systeme , Dresden Center for Free-Electron Laser Science, Hamburg. Acknowledgements. Colorado State University: J.J. Rocca, D. Ryan, M. Purvis

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Stimulated electronic x-ray Raman scattering at XFELs

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  1. Stimulated electronic x-ray Raman scattering at XFELs Nina Rohringer Max Planck InstitutfürPhysikKomplexerSysteme, Dresden Center for Free-Electron Laser Science, Hamburg

  2. Acknowledgements • Colorado State University: J.J. Rocca, D. Ryan, M. Purvis • LLNL:R. London, F. Albert, J. Dunn, A. Graf, G. Brown • LCLS, SLAC:J. Bozek, C. Bostedt, LCLS accelerator / operating team • MPI PKS: V. Kimberg, C. Weninger

  3. Simultaneous fs X-ray diffraction and photo-emission spectroscopy Probingthe electronic structureofthe Mn4CaO5cluster in theoxygen-evolvingcomplexof PS II J. Kern et al, Sciencexpress, 14 February 2013, science.1234273

  4. SASE XFELs have limited temporal coherence Intensity [a.u.] Time [fs] LCLS bandwidth at 1keV photon energy: Dw= 6-9 eV Coherence time: 0.3 - 0.5 fs 1st measurement: I. A. Vartanyantset al., Phys. Rev. Lett. 107, 144801 (2011)

  5. A route to nonlinear spectroscopy with x-rays Photoionization atomic inner-shell x-ray laser X-ray amplification and wave-packet dynamics in molecules Stimulated x-ray Raman scattering in atoms I(w) w w Ne+ Ne Rohringer et al., Nature481, 488 (2012) C. Weninger et al., under review (2013) Kimberg & Rohringer, PRL 110, 043901 (2012) Upcoming experiments: LCLS, Feb. 2014 FLASH, Oct. 2014

  6. 1sttheoreticalconceptof an atomic x-raylaserPopulation inversionby inner-shellphotoionization 1st X-ray laser proposed back in 1967: Duguay &Rentzepis, Appl. Phys. Lett. 10, 350 (1967). 1st realization in the optical regime (blue laser): Silfvast et al., Opt. Lett. 8, 551 (1983). Fast, powerful x-ray pump required to beat Auger decay ! Ultrafast ionizationof inner-shellelectrons

  7. Photo-ionization inner-shell x-ray laser, NeonCoherent amplification of fluorescence Focused XFEL beam Atomic x-ray laser (amplified spontaneous emission) Atomic gas volume Duguay & Rentzepis, Appl. Phys. Lett. 10, 350 (1967). N. Rohringer & R. London, PRA 80, 013809 (2009)

  8. Schematic experimental setup Grating spectrometer Gas cell filled with Neon grating LCLS beam focusing chamber grating spectrometer AMO high-field chamber Hutch 1 (AMO) Hutch 2 (SXR) Diagnostics: - Inline spectrometer for monitoring transmitted XFEL and amplified scattered x rays - Grating spectrometer for scattered/fluorescent xrays

  9. Single shot of highest intensity: 8×109 photons in Ne K-a linecorresponding to GL 21-23 FWHM 2 eV (instrumental resolution) FWHM 10 eV Gas pressure: 500Torr Focal radius: 1-2 mm Interaction length: 1.6 cm Rohringer et al., Nature481, 488 (2012)

  10. Pumping-power dependence of Ne K-a transition (every point corresponds to an average over 10 LCLS shots) Average GL = 19-21.3 @ pulse energy of 0.25 mJ Rohringer et al., Nature481, 488 (2012)

  11. A route to nonlinear spectroscopy with x-rays Photoionization atomic inner-shell x-ray laser X-ray amplification and wave-packet dynamics in molecules Stimulated x-ray Raman scattering in atoms I(w) w w Ne+ Ne Rohringer et al., Nature481, 488 (2012) LCLS, Sept. 2010 C. Weninger et al., under review (2012) LCLS, Aug. 2011 Kimberg & Rohringer, PRL 110, 043901 (2012) Upcoming experiments: LCLS, Feb. 2014 FLASH, Oct. 2014

  12. X-ray pumping of Neon near the K-edge LCLS bandwidth: 7 eV 3p 2p 2p 2s 2s [1s]3p 867.2 eV 1s 1s 3 eV [1s]4p 868.8 eV FWHM 0.27 eV D. V. Morgan et al., PRA 55, 1113 (1997) Total ion yield

  13. Stimulated Electronic X-ray Raman Scattering 3p 2p 2p 2s 2s K edge 1s-3p 1s 1s 7 eV FWHM K edge 1s-3p Weninger et al., under review (2013)

  14. Emitted line profile as a function of pump photon energy K edge Weninger et al., submitted (2013)

  15. Stochastic line shift due to “anomalous” linear dispersion of resonance scattering wout 1st RIXS experiments on Cu with Synchrotron radiation (1976) Continuum win Detuning, D wout win P. Eisenberger, P.M. Platzman, H. Winick, PRL 36, 623 (1976). Width of resonance: 0.25 eV Width of SASE spike: Dw=1/t =0.1 eV

  16. Master Equations for atomic and ionic density matrices coupled to Maxwell’s equation

  17. Effective sRIXS cross section as a function of propagation depth RIXS processdominatedby 5 spectralintensityspikes – 5 distinctmodes in theemittedspectrum

  18. Simulated spectral / temporal intensity profiles of sRIXS process

  19. Simulated Single-Shot Raman Spectra Coupled generalized Maxwell-Bloch equations K edge

  20. Line profile – comparison of experiment to simulation Theory Experiment K edge Weninger et al., submitted (2013)

  21. Raman Signal Strength as a Function of Pump Energy Numberofseedphotons: 103-104 (varying due to spectralsidebandsofthe XFEL) Estimatednumberofphotonsofspontaneous RIXS: 100 Saturatedamplificationby 7-8 ordersofmagnitude Weninger et al., submitted (2013)

  22. High-resolution x-ray Raman spectroscopy by statistical analysis (covariance mapping) Covariance map from 5000 simulated single-shot spectra Weninger&Rohringer, in preparation

  23. Self-stimulated x-ray emission processes in diatomic molecules Core-excited, dissociative Core-ionized Core-ionized Atomic lasing XFEL pump X-ray emission Valence excited Valence dissociative XFEL pump X-ray emission Ground Ground Ground Kimberg & Rohringer, PRL. 110, 043901 (2012). XFEL pump Q. Miao, J.-C. Liu, H. Agren, J.-E. Rubensson & F. Gel’mukhanov, PRL 109, 233905 (2012). Victor Kimberg

  24. Photo-ionization X-ray lasing scheme in molecular Nitrogen Fluorescence spectrum 2Su+ 3sg-1 3sg-1 1Sg+ [1] B. Kempgens, et al. J. Phys. B 29, 5389 (1996) [2] P. Glans, et al. J. El. Spec. Rel. Phen. 82, 193 (1996)

  25. Alignment of the molecule matters Impulsive (field-free) laser alignment of the molecular ensemble alignedensemble <cos2q>=0.8 E q isotropicensemble Contours of the 3sg orbital (final state) Number of emitted x-ray photons as a function of the incoming XFEL photon number (50 fs pulse duration, 1.5 mm focus)

  26. Impulsive laser alignment Degreeofalignmentforvariouslaserparametersandtemperatures Alignedensemble 800 nm, 110 fs, 6x1013 W/cm2 : 1 – 100 K : <cos2q>=0.62; 0.164 2 – 300 K : <cos2q>=0.5; 0.22 800 nm, 100 fs, 1x1014 W/cm2 : 3 – 100 K : <cos2q>=0.70 4 – 50 K : < cos2q>=0.77 Anti-Alignedensemble

  27. Emission spectra for two different electronic final states <cos2q>= 0.5 <cos2q>=0.77 3sg-1 <cos2q>=0.22 1pu-1 fluorescence spectrum

  28. Stimulated X-ray Raman scattering to study charge transfer Start valence/vibrational wavepacket at atomic site A Dt Dt “charge transfer” Probe at atomic site B w1 w3 w2 ws S. Mukamel et al. ( PRL89, 043001 (2002), PRB 72, 235110 (2005); PRA 76, 012504 (2007); PRB 79, 085108 (2009)

  29. Evolution of emitted spectrum FEL input: transform limited 5 fs pulse, 2.5 x 1012photons (LCLS II) Emission shift to w=2w00-w22 Shift of emission frequency due to 4-wave mixing Saturation broadening Onset of saturation Propagation depth [mm] Kimberg & Rohringer, PRL. 110, 043901 (2012). Energy [eV]

  30. Stimulated x-ray Raman scattering creates Vibrational and electronic wave-packet Intermediate state Time [fs] normalized 1 0.1 0.01 Internuclear distance [a.u.] Internuclear distance [a.u.] normalized Time [fs] Final state Internuclear distance [a.u.] Internuclear distance [a.u.]

  31. Different ways to for stimulated X-Ray Raman scattering Two-color Raman scattering with seeded source Pick 2 distinct frequencies within 10 eV SASE bandwidth allows selection of intermediate and final state Impulsive Raman scattering with seeded source “attosecond pulses”, broad bandwidth transform limited pulse (10 eV bandwidth, 0.25 fs pulse duration) Impulsive Raman with broadband SASE temporal resolution limited to coherence time of source for non-linear processes depending on higher-order field correlation functions N. Morita and T. Yajima, PRA 30, 2525 (1984). Y. H. Jiang et al., PRA 81, 051402(R) (2010). M. Belsley et al. PRA 64, 063806 (2001). K. Meyer et al., PRL 108 098302 (2012),

  32. Two-color SASE XFEL operation Relative separationofthepulses: ≈ 2% ofcentralphotonenergy SASE bandwidthofeachindiviual pulse: ≈ 0.5% ofcentralphotonenergy Twopulsescanbedelayedwithinelectronbunchlength Lutman et al., Phys. Rev. Lett. 110, 134801 (2013).

  33. Simulated sRIXS spectra on p* resonance in CO using two-color SASE mode preliminary Intensity [arb. units] stimulatedemission stimulatedemission on „elastic“ peak Photon energy [eV] Challenge: Find regimeofbestsignalcontrast ( to at least 10% change)

  34. Summary and Outlook New Results Stimulated x-ray emission processes are accessible at XFELS 1st atomic inner-shell x-ray laser based on photoionization 1st demonstration of stimulated (impulsive) electronic x-ray Raman scattering Directions Transfer of stimulated emission processes to molecules (gas phase) 2 upcoming experiments in 2014 Feasibility studies of stimulated x-ray Raman scattering in liquids and solids Opportunities Use XFELs to pump electronic/vibrational wave packets Development of new all x-ray (and x-ray / optical) pump probe techniques Nonlinear x-ray spectroscopy

  35. Postdoctoral position in experimental AMO physics available in our group at CFEL in Hamburg nina@pks.mpg.de Project: demonstrate a molecular x-ray lasing and stimulated RIXS in CO and N2 at 2 upcoming beam-times at the LCLS and FLASH XFEL

  36. Outlook for stimulated X-ray Raman scattering in molecules at SASE XFELs • sRIXS in forwarddirection: • in principle high energyresolution, limited byspectralcoherencof SASE pulses • only limited access to transitionsof different symmetry • strong pre-edgeresonance • seedingwithtailsof FEL pulses not possible • two-color SASE schemenecessary • covariancemapping: probably not sufficient to measurethetransmittedspectrum • need to measuretheincoming SASE spectrum – crosscorrelation • goodcontrolof relative intensitiesofthetwo SASE modes • Rydbergstates: currentlybeinginvestigated • wesuspecthighergainsdespitesmaller pump dipoletransitionstrength

  37. Polarization of emitted radiation control by pre-aligned sample Example: transitiondipoleparralel to molecularaxis opticalalignmentlaser a a XFEL

  38. Pumping power requirements for x-ray lasers E2,N2,g2 Dn Population inversion: l,n, A21 Gain coefficeint: E1,N1,g2 E0 Einstein A coefficient: Required pump power density to compensate for level depletion: Naturally broadened transition (rad. decay): Pumping power to maintain a specific gain: J. J. Rocca, Rev. Scient. Instr. 70, 3799 (1999).

  39. Small-signal gain cross section Single shot – versus ensemble average FWHM20 fs Gain at gas density of 1.6e19 atoms/cm3: G=rs =64 cm-1

  40. Slow-down of group velocity on resonance Gain-guiding, due to absorption of pump occupation of upper state normalized No pump absorption occupation of upper state normalized normalized (see also Casperson & Yariv, PRL 26, 293 1971)

  41. Evolution of bond-length in excited and final state for a pump pulse of 50 fs Population of Intermediate (core-excited) state Bond-length of intermediate state Bond-length of final state Incoherent superposition Of final vibrational states Kimberg & Rohringer, PRL. 110, 043901 (2012).

  42. Fine Tuning of the emission v=2 V=1 Emission energy (eV) v=0 Interaction length (mm)

  43. Evolution of XFEL pump pulse and emitted XRL pulse through the gain medium SASE Pulse 1 SASE Pulse 2 XFEL XFEL distance [mm] distance [mm] XRL XRL normalized distance [mm] distance [mm] normalized

  44. Beam profiles of LCLS and XRL in the far field FEL and XRL have the same angular divergence, ~ 1 mrad Rohringer et al., Nature481, 488 (2012)

  45. The build-up of transform-limited pulses Gaussian pulse, 40 fs, 2 x 1012 photons; Length: 16 mm, Density: 1.6 x 1019 cm-3 1.e12 1.e08 Saturated gain region Number of photons 1.e04 Linear gain region 1.e00 no spectral gain narrowing transform limited pulses Weninger & Rohringer, in preparation see also: Hopf et al., PRL 35, 511 (1975); Hopf & Meystre, PRA 12, 2534 (1975)

  46. Vibrational and electronic wave-packet dynamics Intermediate state z= 3 mm (exp. gain regime) normalized Time [fs] Time [fs] Internuclear distance [a.u.] Internuclear distance [a.u.] Time [fs] normalized Time [fs] final state Internuclear distance [a.u.] Internuclear distance [a.u.]

  47. X-ray absorption cross section N2

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