Time Resolved (Pump Probe) Experiment to watch structural dynamics by using the pulsed nature of synchrotron radiation

Transcription

1 SESAME-JSPS School November 14-16, 2011 Amman, Jordan Time Resolved (Pump Probe) Experiment to watch structural dynamics by using the pulsed nature of synchrotron radiation Shin-ichi Adachi (Photon Factory, KEK)

2 Time Resolved (Pump Probe) Experiment Motivations Can we visualize structural dynamics at atomic scale by using synchrotron radiation? Can we watch a molecular movie?

3 An Example: Oscillating chemical reaction Briggs-Rauscher reaction I 2 I - 50mM KI, 38mM malonic acid, 5mM MnSO 4, 0.88M H 2 O 2, 35mM perchloric acid, 0.01% starch

4 Outline of the talk 1. What is pump-probe method? 2. Pump-probe method with SR 3. Examples 4. Concluding remarks

5 Outline of the talk 1. What is pump-probe method? 2. Pump-probe method with SR 3. Examples 4. Concluding remarks

6 What is pump probe method? In a typical pump-probe experiment, the light for excitation ('pump') modulates the initial state, and the light for measuring ('probe') captures the snapshot. Center for Molecular Movies

7 Pump probe method as a tool for making movies (1) We want to watch something moving. Case 1: 2: Continuous Pulsed Light Light probe light rotation of the disk 0 time Disney

8 Pump probe method as a tool for making movies (2) Watching the 6 guys dancing. Disney

9 Pump probe method as a tool for making movies (3) Continuous vs. Pulsed Light Case 1: Continuous Light Case 2: Pulsed Light Pump-probe movie probe light probe light rotation of the disk rotation of the disk 0 time 0 time

10 Pump probe method as a tool for making movies (4) Disney Still image static structure Movie dynamic mechanism

11 Summary #1 What is pump probe method? The pump-probe method enables us to make movies. We need pulsed light for it. Timing between the pump and the probe must be synchronized.

12 Outline 1. What is pump-probe method? 2. Pump-probe method with SR 3. Examples 4. Concluding remarks

13 The pulsed nature of SR (1) You learned that the synchrotron radiation is pulsed light source. I emphasize the importance of this feature again for pumpprobe method.

14 The pulsed nature of SR (2) SR movie Institute for Storage Ring Facilities Electron Injection, Storage and Synchrotron Radiation Light Generation in the Storage Ring ASTRID. (Credit: Coldvision Studio/ISA)

15 Why electrons are bunched? Acceleration of electrons with DC or AC voltage RF cavity V(t) DC = voltage Vsin t -V GND e - Synchrotron storage ring (period of 1 turn) / (period of RF acceleration) = N (harmonic number)

16 The pulsed nature of SR (1) Why electrons are bunched? (phase stability) Acceleration Deceleration RF field V(t) E E s s T>T rf : Heavier electron takes more time. T rf T>T rf : Lighter electron takes less time. t s s : stable phase

17 The pulsed nature of SR (2) synchrotron oscillation V(t) T rf e - RF cavity V(t) = Vsin t Synchrotron ring E s s s t

18 How short is the pulse duration? e - Storage Ring Q: Bunch length in SR is typically 30 mm (1 sigma). How short is the pulse duration? A: 30 x 10-3 / (3 x 10 8 ) = 100 x (s) = 100 (ps)

19 utilizing pulsed nature of the synchrotron radiation for structural dynamics studies Bunch length ~ 15 mm ~ 50 ps

20 Synchronization between pump and probe pulses RF Master Oscillator MHz RF Amplifier Phase Shifter Counter 1/6 84.7MHz Counter 1/89600 Mode-locked Ti:S laser 945 Hz Delay Generator Regenerative Amplifier Laser Booth RF cavity Counter 1/ kHz Counter 1/ Hz 800 nm 945 Hz 150 fs NW14 Experimental Hutch PF-AR NW14 Undulator 794kHz X-ray Pulse Selector 5-20 kev 945 Hz 100 ps X-ray detector

21 TR X ray Diffraction (1 khz mode) timing chart X-ray from PF-AR (794 khz = 508 MHz / 640) 1.26 sec X-ray Pulse Selector (945 Hz = 794 khz / 840) X-ray at Sample (945 Hz) open close 1.06msec Diffraction signal (945 Hz) Laser pulse (945 Hz) delay

22 picosecond time-resolved x-ray techniques a basic concept synchrotron radiation x rays: structural studies at atomic resolution diffraction, XAFS, scattering, etc pulsed nature of SR: time resolution ~50ps = molecular movies at atomic and ~50ps resolution

23 Outline 1. What is pump-probe method? 2. Pump-probe method with SR 3. Examples 4. Concluding remarks

24 photo-induced structural dynamics visual sensing biology and chemistry photosynthesis ultrafast photo-switching materials, energy and environment solar cell

25 Picosocond X ray applications at KEK Picosecond photoresponse of perovskite manganite (NSMO) thin film (TR Diffraction: t~ 50ps ~ 2ns) Photo induced spin crossover transition of metal complex in solution (TR XAFS: t ~700ps) Ichikawa et al. Nature Materials, 10, 101 (2011) Nozawa et al. J. Am. Chem. Soc., 132, 61 (2010) Photochemical reaction in liquid (TR solution scattering: t~100ps~1ms) Ligand migration dynamics in protein crystal (TRprotein crystallography: t~800 min) Laser shock induced lattice deformation of CdS single crystal (TR single shot Laue diffraction: t~1ns~10ns) Tomita et al. Proc. Natl. Acad. Sci. USA, 106, 2612 (2009) Ichiyanagi et al. Appl. Phys. Lett. 91, (2007)

26 Ultrafast structural dynamics of Fe complex revealed by TR XAFS Nozawa et al. J. Am. Chem. Soc., 132, (2010). Open Jet system Shunsuke Nozawa (KEK) Tokushi Sato (KEK) Laser pulses 945 Hz Fluorescence X-ray X-ray 794 khz (Energy-scanned )

27 picosecond spin transition of Fe II (phen) 3 LS state S=0, 1 A 1 HS state S=2, 5 T 2 e g Fe 2+ (phen) 3 3d 6 10Dq Octahedral FeN 6 t 2g 1 MLCT 400nm MLCT,LF FeN 6 cluster Energy 1 A 1 (LS) ~700ps 5 T 2 (HS) Fe N bond length R LS < Fe N R HS Fe N Fe N bond length

28 X-ray Absorption Fine Structure (XAFS) Cu K-Edge (Cu foil, 5 m thickness) Near Edge Structure (XANES) 1s -> 3d, 4p states Spin and electronic states Extended Fine Structure (EXAFS) 1s -> unbound states Photoelectron Scattering -> structural info

29 TR-XAFS: Experimental Setup

30 Excite state XANES Fe K-edge XAFS Fe(phen) 3 Aqueous Solution C D Time Course Feature B Intensity (arb. units) A B difference x 15 Intensity (arb. units) ± FWHM 142 ps X-ray = 60 ps I = I 0 exp[-( t/ )] = ps Low Spin Transient difference at +50ps Time Course Feature D Photon Energy (ev) Delay (ps)

31 Excited state EXAFS Energy 1 MLCT 400nm 1 A 1 MLCT,L F 5 T 2 (HS) (LS) ~700ps Fe N bond length Intensity (arb. units) 6800 Fe K-edge EXAFS LS Transient difference (+50ps) difference Photon Energy (ev) Fourier Transform Distance R (A) LS transient HS (+50ps) 3 4 EXAFS analysis summary Spectrum R Fe-N (A ) 2 (A 2 ) LS 1.98(1) 0.001(1) Photo-excited HS 2.15(2) 0.011(3)

32 Picosecond molecular movie! Low Spin Ground State ( 1 A 1 ) Photo- Excited High Spin State ( 5 T 2 ) 1.98A 2.15A ~700 ps Nozawa et al. J. Am. Chem. Soc., 132, (2010).

33 Concluding remarks Pump-probe method with synchrotron radiation enables us to make molecular movies at atomic spatial resolution and picosecond time resolution. (Next generation light source (FEL, ERL) will provide femtosecond time resolution.) The pump-probe method is applicable to most of synchrotron measurements. This will be fun!