Background and Present Status from AMO Instrument Team

Transcription

1 Background and Present Status from AMO Instrument Team 1. Team Organization. 2. Proposed Scientific Plan. 3. The First Experiment. 4. Future Plan.

2 Historical Facts April 2004: LCLS puts out a call for Letters of Intent (LOI) category A: science & end-station construction category B: science category C: instrument design July 2004: LCLS SAC makes recommendation that two AMO proposals of the category A LOI collaborative teams merge October 2004: Ultra-fast science workshop

3 October 2004: Ultra-fast science workshop Workshop Objective: solicit input & participation from the AMOP community for the LCLS project - shape the scientific program: Scientists ideas - help define the critical XFEL machine parameters - help define the designs of an AMOP end-station(s) - interaction of the five collaborative teams Five LCLS collaborative teams: - Atomic, Molecular & Optical Science - Optical pump x-ray probe studies in chemistry, biology & material science - Diffraction imaging of single objects approaching atomic scale resolution - Coherent x-ray scattering for the study of dynamics - High-energy density science

4 AMO Collaborative Team ( Original Merged LOIs A) Marriage of Synchrotrons + Ultrafast Communities Lou DiMauro (OSU) & Nora Berrah (WMU) (co-t. Leaders) John Bozek (Instrument Scientist) Pierre Agostini OSU John Bozek LBL Roy Clarke UM Paul Fuoss ANL Chris Greene U Colorado Bertold Kraessig ANL Dan Neumark UC Berkeley Steve Pratt ANL John Reading Texas A&M Steve Southworth ANL Linda Young ANL Musahid Ahmed LBL Philip H. Bucksbaum SU/SLAC Todd Ditmire UT Austin Ernie Glover LBL Elliot Kantor ANL Steve Leone UC Berkeley Gerhard Paulus Texas A&M Alexei Sokolov Texas A&M David Reis UM Linn Van Woerkom OSU ~ Twenty Additional Scientists Expressed Interest at the October 2004 Workshop

5 Update on AMO Organization/Activities 1. Instrument Scientist, John Bozek, Hired (Jan 2006) 2. Regular Teleconference (Berrah, Bozek, DiMauro, Young) 3. N. Berrah on Sabbatical FY06 4. Periodic visits by DiMauro/Berrah 5. Communication with Broader Team at Conferences (Wisconsin W. 8/04; DOE M. 9/05; DAMOP 5/06) 6. Updates to Broader Team when Necessary (seek input, communicate news) Discussions/communication led to determine the instrumentation needs for first experiments! 7. Conceptual Design and Instrument Budget was submitted and Accepted by LCLS.

6 Update on AMO Activities/ Organization (cont..) 8. Synergy between the PULSE Center and AMOS 9. Workshop to Stimulate Theory (ITAMP 06-06) 10. Met with: -----LCLS Optics Group Pump-Probe Team to Explore Common Interest and will Continue to Meet. 11. Plan to Meet with Imaging Group to Explore Shared Experimental System? 12. Held Ultrafast x-ray Summer School June 2007

7 Team Major Scientific Thrusts: Multiphoton and High-Field X-Ray Processes in Atoms, Molecules, Clusters,& Biological Molecules. Time-Resolved Phenomena in Atoms, Molecules (bio-molecules) and Clusters using Ultrafast X-Rays

8 AMO LOIs Collaborative Team Science: 1. Multiple core excitation in atoms, molecules and clusters 2. Timing experiments: Inner-shell side band experiments Photoionization of aligned molecules Temporal evolution of state-prepared systems 3. Nonlinear physics 4. Ion (positive/negative) studies 5. Pump-probe, X-X or X-laser or X-e 6. Raman processes 7. Cluster dynamics (Diffraction of size-selected clusters) 8. Photoionization dynamics of biomolecules

9 Science discussed at 2004 October AMOS forum Ken Taylor (Ireland) David Reis (UM) Robin Santra (ITAMP) Anders Nielsson (SSRL) Chris Greene (UCB) John Bozek (ALS, LBNL) Ali Belkacem (LBNL) Keith Nelson (MIT) Ernie Glover (LBNL) Elliott Kanter (ANL) Possibilities for few- and many-electron atoms & ions in XFEL pulses Synchronization issues for pump-probe experiments at LCLS Cluster physics at high photon energies Time resolved spectroscopy for studies in surface chemistry and electron driven processes in aqueous systems Multiphoton ionization processes in free atoms and clusters Atoms, molecules, clusters and their ions studied with two or more Photons Inner-shell ionization and de-excitation pathways of laser-dressed atoms and molecules Give him 10 minutes max and then let's get back to reality X-ray/optical wave mixing Hollow neon atoms

10 LCLS Characteristics The LCLS beam intensity (~10 13 x-rays/200 fs) is greater than the current 3rd generation sources (10 4 x-rays/100 ps). Extreme focusing (KB pairs) leads to intensity ~10 35 photons/s/cm 2 (~ W/cm 2 for 800 ev x- rays) Nonlinear and strong-field effects are expected when the LCLS beam is focused to a spot diameter of 1μm. BUT, electron s ponderomotive (quiver motion) important at low frequencies IS negligible in the x-ray regime (λ 2 ).

11 AMOS Inst.Team Short-Long Range Plans: High Field: Using the extremely high brightness of the LCLS we propose to study: multiple ionization atoms & simple molecules with angle-resolved spectroscopy and ion imaging to understand basic phenomena in highly excited matter High-field photoionization in clusters (of various types) Low density ionic targets: atoms, molecules, fragments, clusters, biomolecules by photoelectron and ion imaging techniques Time-Resolved: Temporal resolution will be used to perform: Inner-shell photoelectron spectroscopy of molecules (pump-probe using lasers) into specific states. Inner-shell photoelectron imaging of isolated biomolecules to follow their chemistry in natural time scale

12 Double K Vacancy in Gas-Phase Systems Possible Consequences The decay of the KK-vacancy state will produce higher charge states This process extensive fragmentation in molecules This process damage consideration in experiments on Bio-molecules?

13 LCLS High Field Beam will Probe: Auger Decay Auger Decay Sequential (or Cascade ) Multi-Auger Decay Photodetachment (or Ionization) Simultaneous Double-Auger Decay ( 3-10% of single Auger)

14 Some Examples High Field Studies in Atoms

15 X-Ray Strong Field Experiment x-ray multiphoton ionization photoionization correlated ionization Auger sequential 2-photon, 2-electron

16 Low-Frequency Physics High Frequency IR: Low frequency regime VUV FEL: Intense photon source XFEL FEL: Highly ionizing source -I p -I p -I p 10 x20 W/cm W/cm 2 Keldysh parameter γ <<1 Tunnel / over the barrier ionisation Ponderomotive energy ev W/cm 2 Keldysh parameter γ >>1 Multi-photon ionisation Ponderomotive energy 10 mev Angstrom wavelength Direct multiphoton ionisation Secondary processes γ Optical Frequency = (I p /2U p ) 1/2 λ -1 ; U p =I/4ω 2 (au) Tunneling Frequency

17 Intensity, Wavelength and Ponderomotive Energy (Lambropoulos) λ (nm) ћω (ev) U p (ev) I (U p ћω ) W/cm

18 FLASH Experiments PRL 94, (2005) Theory Available! Calculate the rate of production of highly charged Xe i+ ions produced by direct multiphoton absorption, to compare with experiment.

19 TOF Spectrum for Atomic Xenon Multiphoton Ionization (Wabnitz et al. 05 )

20 Wabnitz et al. 05

21 First LCLS Experiment: K-Shell in Ne 1. Photoionization 2. Auger Decay 3. Sequential Multiphoton Ionization 4. Direct Multiphoton Ionization LCLS Theory: Double-K ionization in Ne due to absorption of 2-photons by 1 atom for hγ>932 ev is predicted to be 100%

22 Ne K-edge ~ 870 ev The probability of twophoton absorption by 1s 2 - shell accompanied by the creation of double 1svacancies predominates over the probability of the process of two-photon oneelectron excitation/ionization of the 1s 2 shell in the range of x-ray photon energies 930 ev. 2 e-out 1e-out

23 Ne Charge State vs Intensity Rohringer & Santra, PRA 76, ev

24 Probable Ne Charge State with beamsize Rohringer & Santra, PRA 76, (2007)

25 Power of TOFs: Inner-Shell Resonances in Ar; 2 p Excitation to Rydberg States(ALS) LCLS: K-Shell Ar How would the ratio of Doubly Ionized Ions (Auger decay) Compares to Singly Ionized Ions due to spectator Auger decay? Resonant shake-off of two electrons.

26 High Field Studies in Molecules

27 Resonant Auger Electron Spectroscopy Interesting in molecules too CO resonant Auger:

28 Probe Auger(2+)/Spectator Auger (1+) Decay & Fragmentation Pathways Spectator Auger

29 HBr 3d (ALS) Excitation/Ionization 2D Map; Angle- Resolved;e- TOFs LCLS: HBr, Br 2 2p & 2s Ionization

30 Ion Imaging : Fragmentation Decay Channels of CO 2 2+ Subsequent to K- Shell Photoionization and Auger Decay of CO 2. Identify different fragmentation mechanisms

31 Fragment Momentum Correlation Plots: Fragmentation Decay Channels of CO 2 2+ Subsequent to K-shell Photoionization and Auger Decay of CO 2.

32 High Field Studies in Clusters

33 Cluster Studies at FLASH in Hamburg

34 Cluster Studies, FLASH Xenon Cluster size 2500 atoms Intensity (arb. units) Xe 2+ P FEL =2.5*10 13 W /cm 2 T 8 76 puls =50 fs λ FEL =98 nm 6* *10 11 Unusually high energy absorption in cluster Fragmentation starting at W/cm 2 8*10 10 Xe Time of flight (ns) 2*10 10 Wabnitz et al, Nature 420, 482 (2002)

35 Molecular dynamics simulations indicate that standard collisional heating cannot fully account for the strong energy absorption.

36 In contrast with earlier studies in IR and VUV spectral regime, we find NO evidence for electron emission from plasma heating processes; Multistep ionization process is dominant hν=37.8 ev, <N>~100, I=3x10 13 W/cm fs

37 Proposed at LCLS: Ion, e-, and Scattering Experiments on Clusters Study the Dynamics of Cluster Explosion as a Function of Cluster Size, Wavelengths, Intensity: Is it a Coulomb Explosion Picture (as in intense optical or near IR ultrafast laser pulses) OR Explosion due to Hot Nanoplasma (multiple scattering from the cluster atoms can confine electrons yielding a nanoplasma); Explosion Time can be Different OR, New mechanisms?? Will Collective Electron Effects be important as in the dynamics of IR irradiated large clusters?

38 n1 4d Photoelectron Spectrum of Xe Clusters at hν=135 ev

39 Slide 38 n1 berrah, 6/3/2008

40 Velocity Map Imaging Coincidence System ALS Electron Detection Ion Detection 80 mm position-sensitive multi-hit hexanode detector (Roentdek) Rolles et al. Nucl. Instr. and Meth. B 261, 170 (2007).

41 Fragmentation of Rare Gas ALS

42 n2 PEPIPICO coincidence map for photoionization at hv=216 ev

43 Slide 41 n2 berrah, 6/3/2008

44 High Field Studies in Ions

45 Movable Ion-Photon Beamline for ions & size-selected clusters Size Selected Production Size and Charge Selected Detection Absolute cross sections: measurements of overlaps, photon & ion fluxes and detector efficiencies.

46 High Charge State Formation Following 2p Photodetachment of S - (ALS) LCLS: S K-shell S 2+ /S + 60% Li 3+ /Li 2+ <1% PR A 72, (R), 05 Th, Sim-Auger Int, K-Out H, S-Off; S-Up+Seq-Aug

47 Ion Studies: Measure electron spectra of ionic species Si - S + Si + Si 2 + Si 3 +

48 Photoionization Dynamics of Clusters or Biomolecules Biomolecules injected via electrospray

49 Time-Resolved Studies of Molecules Pump-probe experiments of molecules (state-selected): - Launch a molecule on a particular potentially energy surface - Watch temporal evolution with angle-resolved inner-shell PES

50 Photodissociation Dynamics of I 2- : Pump-Probe Experiments Short delay times photodetachment accesses bound vibrational levels of I 2 states Longer times, dissociation to I - + I I 2 Complete dissociation photodetaching free I - LCLS, Probe with >800 ev photons I 2 -

51 Photodissociation Dynamics of I 2-2P 1/2 and 2P 3/2 spin-orbit states of I. I - photoelectron spectrum Neumark et al. Chem. Phys. Lett, 258 (1996) 523.

52 Photodissociation Dynamics of I 2 - I 2 P 3/2 Dissociation Time scale: Rise time of electron signal reaches 50% of its maximum value by 100 fs. I 2 P 1/2

53 END

54 Molecular Fragmentation: Ion Momentum Imaging of Molecules (ALS)

55 Photodissociation Dynamics of I 2 - Kolsoff et al.