Attosecond Science (1) (1)

Transcription

1 Kenichi Ishikawa ( ) ishiken@atto.t.u-tokyo.ac.jp Advanced Plasma and Laser Science E Attosecond Science (1) (1) 1

2 m n f a (m/s) (s) = (m) = 9 µm 2

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4 800nm (optical cycle at 800 nm) m/( m/s) = s = 2.7 fs 4

5 atomic unit of time = 24 attoseconds Orbital period of the Bohr electron mω 2 r = 1 4πϵ 0 e 2 r 2 T = 2! =2 r 4 0 mr 3 e 2 = 152 as = 2 a.u. real-time observation and time-domain control of atomic-scale electron dynamics 5

6 Dynamics of the Auger effect Delay in photoemission Direct measurement of light waves 6

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8 Ejection of a core electron Instantaneous Core-excited ion ~ a few fs Ejection of a valence electron Observation of the ejection of Auger electrons Ionizing X rays < a few fs Attosecond pulse 8

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11 E(t) = E 0 (t) cos(ωt + φ) dp dt = mdv dt = ee(t) ionization at t = t r Initial momentum p 0 = 2m( hω X I p ) Momentum at the detector p = p 0 + p p = e E(t)dt = ea(t r ) ee 0(t) sin(ωt r +φ) = 4mU p (t r ) sin(ωt r +φ) ω t r Kinetic energy at the detector W W 0 + p 0 p m = W 0 + 8W 0 U p (t r ) sin(ωt r + φ) 11

12 W W 0 + 8W 0 U p (t r ) sin(ωt r + φ) Electron kinetic energy Ejection time 12

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15 The photoelectric effect is usually considered instantaneous. Ne Ne + e t 2s 2p Ne 2s Short light pulse Ne t 2p Ne + e 15

16 rent experimental parameters, the small deviations between the electron s exactmotionand that modeled via the CVA give rise to a 2-as discrepancy in the relative delay. Accepting this small discrepancy, manyelectron models were applied to investigate the effects of electron correlation. As a first attempt, the multiconfigurational Hartree-Fock method was used to evaluate transition matrix elements from the ground state of Ne to states where the electron wave asymptotically propagated along the direction of the streaking NIR electric field. These time for allowing us to track the history of microscopic phenomena accurately (Fig. 1A) calls for precise knowledge of the delay between the XUV pulse and an outgoing electron wave packet (henceforth, absolute delay). This can only be inferred from theory. For multielectron systems, such as Ne, physical description of the discrepancies revealed by this work proved to be a challenge. The sensitive experimental test to which time-dependent manyelectron models can now be subjected will benefit their development. measure only re photoemission c lute delays relies tested time-dep Presently, only tw provide this deg photoionization cause of low S/N complex system of the photoelect streaking will atomic photoion sensitive tests, w ually improving predictions. Thes understanding of and will make t atomic chronosco Schultze et al., Science 328, 1658 (2010) Fig. 3. The relative delay betweenphotoemissionfromthe2p and 2s subshells of Ne atoms, induced by sub 200-as, near 100-eV XUV pulses. The depicted delays are extractedfrom measuredattosecond streaking spectrograms by fitting a spectrogram, within the strong-field approximation, with parameterized NIR and XUV fields. Our optimization procedure matches the first derivatives along the time delay dimension of the measured and reconstructed spectrograms, thereby eliminating the influence of unstreaked background electrons [for details on the fitting algorithm, see (29)]. From the analysis of a set of spectrograms, the measured delays and associated retrieval uncertainties are plotted against the amplitude of the vector potential applied in the attosecond streak camera. Spectrograms measured in the presence of asatelliteattosecondpulsewerefound to exhibit a less accurate retrieval of the delay value. When a subset of data (red diamonds) that represents scans with less than 3% satellite pulse content was evaluated, a mean delay value of 21 as with a standard deviation of ~5 as was found. The green circles represent the result of analyzing spectrograms recorded with an XUV pulse with narrower bandwidth in order to exclude the potential influence of shakeup states contributing to the electron kinetic energy spectrum. References a 1. H. Hertz, Annal 2. W. Hallwachs, A 3. A. Einstein, Ann 4. E. P. Wigner, Ph 5. C. A. A. de Carv 83 (2002). 6. A. F. Starace, in (Springer, Berlin 7. S. T. Manson, R 8. M. Y. Ivanov, J. (2007). 9. A. Baltuška et a 10. R. Kienberger e 11. M. Nisoli, G. Sa (2009). 12. G. Sansone et a 13. M. Schultze et a 14. E. Goulielmakis 15. M. Hentschel et 16. A. Borisov, D. S Echenique, Che 17. A. L. Cavalieri e 18. A. K. Kazansky, (2009) 19. C. Lemell, B. So A 79, ( 20. J. C. Baggesen, ; and er 21. U. Becker, D. A Photoionization (Plenum, New Y 22. A. Rudenko et a 23. J. Mauritsson et 16

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18 1864 D = ρ B = 0 E + B t = 0 H = J But who ever saw a light field oscillate? 18

19 p = e Momentum change t r E(t)dt = ea(t r ) Kinetic energy at the detector W W 0 + 8W 0 U p (t r ) sin(ωt r + φ) 19

20 Direct proof of the wave nature of light E. Goulielmakis et al., Science 305, 1267 (2004). 20