Exploring ICD and Dynamic Interference by Free Electron Lasers

Transcription

1 Exploring ICD and Dynamic Interference by Free Electron Lasers Lorenz Cederbaum Theoretische Chemie Physikalisch-Chemisches Institut Universität Heidelberg

2 Exploring Intermolecular Coulombic Decay by Free Electron Lasers or How energy deposited by FEL on one site in a medium can be transferred fast to the surrounding

3 How does an isolated excited ion decay?

4 How does an isolated excited ion decay?

5 How does an isolated excited ion decay?

6 ICD L.S. Cederbaum, J. Zobeley, and F. Tarantelli, PRL 79, 4778 (1997) * A + B A + B + + e ICD is a general phenomenon Hydrogen bonded clusters (H 2 O) n, (HF) n van der Waals clusters Ne n, Ne n Ar m, MgNe, CaNe,... even He 2 quantum dots Ultrafast process fs regime Faster with more neighbors Source of LEE biological relevance

7 ICD in water L. S. Cederbaum, J. Zobeley and F. Tarantelli, PRL 79, 4778 (1997). I. B. Müller and LSC, J. Chem. Phys. 125, (2006). O. Vendrell, S. Stoychev and LSC, Chem. Phys. Chem. 11, 1006 (2010).

8 ICD in water Dimer: T. Jahnke, R. Dörner et al., Nature Phys. 6, 139 (10) Electron-ion coincidence experiments Large clusters: M. Mucke, U. Hergenhahn et al., Nature Phys. 6, 143 (10) Sum of electron energy experiments

9 electrons ICD-electrons ICD-electrons KER Photoelectron spectrum ICD generates lowenergy electrons in water exactly in the energy range where electrons are known to cause DNA strand breaks by dissociative attachment.

10 ICD in H-bonded H systems S.D. Stoychev, A.I. Kuleff, and L.S. Cederbaum, JACS 133, 6817 (2011)

11 ICD in H-bonded H systems S.D. Stoychev, A.I. Kuleff, and L.S. Cederbaum, JACS 133, 6817 (2011)

12 ICD in van der Waals clusters R. Santra, J. Zobeley, L. S. Cederbaum, and N. Moiseyev, Phys. Rev. Lett. 85, 4490 (2000). R. Santra, J. Zobeley, and L. S. Cederbaum, Phys. Rev. B 64, (2001). N. Sisourat, N. V. Kryzhevoi, P. Kolorenc, S. Scheit and L. S. Cederbaum, Nature Phys. (2010).

13 Ionization and double-ionization spectra of atomic Ne and Ne 2 dimer In Ne 2 dimer: 'one-site' Ne 2+ Ne 'two-site' Ne + Ne +

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15 Interatomic Coulombic decay in Ne n clusters R. Santra, J. Zobeley, and L. S. Cederbaum, Phys. Rev. B 64, (2001).

16 Exploring ICD by free electron lasers Ph. Demekhin, S. Stoychev, A. Kuleff, and L.S. Cederbaum, PRL 107, (2011).

17 ICD by FEL For ICD: Ph. Demekhin et al., PRL 107, (2011). For Auger in isolated atom: E. P. Kanter et al., PRL 107, (2011).

18 Exploring ICD by free electron lasers At least two photons are needed for the ICD process. ω = ev

19 Exploring ICD by free electron lasers Integral yield of Ne + ion pairs Comparison of yields for a pulse of central frequency ω = ev (two-photon process) and a pulse doubling the central frequency, ω = ev (one-photon process). Same peak intensity.

20 Electron spectra for different pulse durations and intensities

21 Exploring ICD by free electron lasers Contributions to the electron spectrum. There are strong interference effects between the ICD electrons and those produced by direct ionization of the two Ne atoms.

22 Exploring ICD by free electron lasers Measuring the individual contribution of ICD. Total electron spectrum that measured 30 fs after pulse maximum.

23 Exploring ICD by free electron lasers In a laser field at resonant frequency the potential energy surfaces of the initial state and of the excited state possess a light-induced conical intersection even for a diatomic [1]. If decay processes (like ICD) are involved, the surfaces become complex and their intersections are light-induced DICES (Doubly Intersecting Complex Energy Surfaces) [2]. 1 M. Sindelka, N. Moiseyev, and L.S. Cederbaum, J. Phys. B 44, (2011). 2 L.S. Cederbaum, Y.-C. Chiang, P.V. Demekhin, and N. Moiseyev, PRL 106, (2011).

24 Theory Ansatz for the total WF Nuclear WP propagation Molecular Hamiltonian matrix

25 Summary Enhancement of ICD by strong fields: Two-photon absorption is more efficient than one-photon absorption of double frequency (traditional scheme) Sequential two-photon absorption by one subunit competes with the absorption of two photons by two different subunits Coherent superposition of these two-photon ionization mechanisms: two physical mechanisms two different timescales Measurement of the spectrum after a time delay will allow to identify the individual contributions and determine ICD

26 Dynamic Interference Bound-Continuum Scenario Ph.V. Demekhin and L.S. Cederbaum, Phys. Rev. Lett. 108, (2012). For model ion: K. Toyota et al., Phys. Rev. A 76, (2007). Bound-Bound Scenario Ph.V. Demekhin and L.S. Cederbaum, submitted (2012) arxiv: v1.

27 Bound-Continuum Scenario Weak Field What happens if the field becomes more intense? Field Peak Intensity Total wavefunction

28 Exact photoelectron spectrum of the H atom ω = ev 2 2 gt () = exp( t / τ ) ω IP = 40 ev

29 How to understand the surprising findings? To simplify the exact equations we introduce approximations and verify them. Rotating wave approximation Local approximation Stationary phase approximation

30 Local approximation Ground state amplitude in the local approximation AC Stark Shift and ionization rate

31 Local approximation Photoelectron spectrum

32 Stationary phase approximation Stationary phase condition and the spectrum

33 Dynamic Interference Physical meaning of the stationary phase The dressed ground state follows the pulse and electrons of the same energy emitted at different times interfere with each other. The interference pattern is controlled by the shape of the pulse. Easily generalizable to many electron systems.

34 Bound-Bound Scenario Weak Field The initial (I) and intermediate (R) states are coupled resonantly by the field. Here, for stronger fields, the coupling of the states via the laser pulse is responsible for the shift of the dressed levels as a function of time.

35 Dynamic interference in the two-photon ionization of H Electron spectra Ansatz for the total WF

36 Dynamical coupling of resonances 2x2 Hamiltonian Decoupled resonances scenario Spectrum

37 Dynamic interference in the two-photon ionization Physical meaning The two dressed levels ± > = ( I > ± R > )/ 2 are degenerate at low intensity and repel each other at higher intensity. This repulsion follows the pulse and electrons of the same energy emitted at different times interfere with each other.

38 Summary Dynamic interference is a general consequence of the nature of laser pulses, and it is fundamental to the spectroscopy of strong laser fields. Whenever the field-induced couplings between electronic states of a system and hence the energies of the resonantly dressed states possess the time dependence provided by the pulse, the phenomenon of dynamic interference takes place. This is always the case at high laser frequencies. Where can it be seen: Single-photon ionization (due to AC Stark effect) Two-photon ionization (due to resonant coupling) Resonant auger decay (due to resonant coupling) X-ray photoemission (resonant coupling or AC Stark effect)

39 Jürgen Zobeley ICD Robin Santra ICD Simona Scheit dynamics Imke Müller microsolvation cluster Vitali Averbukh decay widths Kirill Gokhberg RICD Spas Stoychev ICD following Auger Nicolas Sisourat He dimer Acknowledgements External collaboration - Theory External collaboration - Experiment Christian Buth XeF n Hans-Dieter Meyer CAP & CAP/CI Thomas Sommerfeld CAP/CI Alex Kuleff electron dynamics Nayana Vaval Propagators/CAP Nikolai Kryshevoi He droplets Ying-Chih Chiang cascades Philipp Demekhin ICD/Dyn. Interfer. Francesco Tarantelli computational techniques Perugia/Italia Nimrod Moiseyev Ne 2 dynamics Haifa/Israel U. Hergenhahn München/BESSY R. Dörner Frankfurt P. Lablanquie Paris E. Rühl Berlin K. Ueda Sendai

40 Extra material

41 Controllability of the dynamic interference

42 Dynamic interference in He Total AC Stark shift:

43 Dynamic interference in the resonant Auger decay N. Rohringer and R. Santra Ph. V. Demekhin and L. S. Cederbaum