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Attosecond light pulses for observing electron correlations in atoms

Learn about the advancements in ultra-short pulse generation and how attosecond light pulses are used to observe electron correlations in atoms. Explore the control and manipulation of atomic photography with these pulses.

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Attosecond light pulses for observing electron correlations in atoms

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  1. Attosecond light pulses for observing electron correlations in atoms Toru Morishita Univ. of Electro-Communications Chofu, Tokyo With S. Watanabe (UEC)and C.D.Lin (KSU)

  2. Improvements in ultra short pulse generation Atto physics started in 21 century! 21st century Asec region U. Keller, Nature 424, 831 (03) + private comm.

  3. Attosecond in Atoms/Molecules • Rotation of molecules： pico (10-12) sec • Vibration of molecules: femto (10-15) sec • Electron motion in atoms/molecules • Classical period of electron in H atom • 2π* 1 au = 150 asec • Real time analysis • Control/manipulate

  4. Atomic photography No ordinary camera can capture the motion of electrons inside an atom. But the advent of ultrafast laser pulses brings the necessary ‘shutter speed’ for snapping them as they tumble between energy levels close to the nucleus. L F DiMauro, Nature 419, 789 (2002)

  5. Electron motions in atoms • Structure of multi-electron atoms Uranium atom，Max　Ｗ　カーボン， 原子力（それは加害者か被害者か） Atom，Wikipedia (Japanese)

  6. Atom or molecule ? • Completely different Born-Oppenheimer (adiabatic approximation) Hartree-Fock (mean filed) Pauli’s exclusion principle，Shell structure Vibration around equilibrium position Overall rotation (1s)2 (2s)2 ... Th , v, j, ...

  7. 1Se 179 1Po 3Pe 178 1De 1Fo 1Ge 3Po 177 1De 1Se 3Do 3De 3Fe 1Do 176 1Po 3Pe 3Fo 3Po 1Se 1De 175 3s3s 3s3p 3s3d 3p3p 3p3d 3d3d Energy levels of Li+(3l3l’) “Molecular” picture “Atomic” picture Hund’s rule E~EN+ ω(v+1)+B[L(L+1)-T2]+GT2 1Se n=1 179 n=2 n=0 1Po 1De 178 3Pe Energy (eV) 1Ge 1Fo 3Fe 3Po 177 3Do 1De 3De 1Se 1Do 3Fo 176 1De 3Pe 1Po n=(v-T)/2 3Po 175 v=N-K-1 1Se T 2 1 2 0 1 0 0 1 1

  8. Correlated motions, 2s21Se and 2p21Se Atomic orbital〔×〕Molecular picture〔◎〕 2s21Se 2p21Se |K=1〉=0.46|2s2s〉 − 0.88|2p2p〉 |K=−1〉=0.88|2s2s〉+0.46|2p2p〉 “1st excited state” w.r.t. θ12 “Ground state” w.r.t. θ12 (θ12) 0 0 θ12 0 θ12 π 0 π θ12 r2 r1

  9. Coherent Sum (Wave packet) |(θ12)|2 Oscillation period 980 asec 0 π 0 θ12 How can we see the correlated electron motion ? θ12 2s21Se 2p21Se r2 r1 (θ12) 0 0 0 π 0 π θ12 θ12

  10. Visualization of electron correlations Hyperspherical coordinates R r2 r1 r2 ψ≈F(R)Φ(α, θ12)D(ΩE) α θ12 z Breathing vibration Rotation r1 Vibration |Φ(α, θ12)|2 Rotation |D(ΩE)|2 ΩE=αEβEγE (polar plots in body-fixed frame)

  11. 2 e coincidence measurement Double ionization T=Tdelay T=0 p2 He** p1 pump probe Ionization yield • Gaussian • 1st order purtarbation • Direct product of the plane waves (Final state) • Velocity gauge Ionization prob dipole Time evolution of the momentum space wave function “Masking” function →１(for T→0)

  12. Bending vibration Period of the vibration:960 asec 27.2 eV,200 asec E1=E2=2.2eV p2 θ12 p1//ε polarization

  13. Vibrational motion, Tomographic imaging 2s21Se + 2p21Se Hyperspherical coordinates in momentume space p2 Rp αp p1 p1 p2 θp12 Ep=27.2 eV, T=200 asec E1=E2=2.2eV

  14. Rotational motion 2s21Se + 2p21De Molecular axis z’ t=1fs t=2 fs t=0 Polar plots Double ionization yield, S z’

  15. Detailed structure in momentum space T=200 asec Ep=54.4 eV Ep=27.2 eV αp θp12 Low energy： 2electrons have the same energy High energy： 1 has most of the energy p1 =p2 p1 <p2 p1 p2 p1 p2 θp12 θp12

  16. Rotation + Vibration Vibration and rotation can be separated Vibration (averaged over rotational coordinates) Rotation (averaged over vibrational coordinates)

  17. Pump-probe experiments • pump　(probability10-3 - 10-4 ) 2 photons 2 color photons Ti:Sa Laser + XUV 480 asec, 38 eV, 4x1012 W/cm2 5 fsec, 1.5 eV, 4x1013 W/cm2 480 asec, 36.7 eV, 4x1014 W/cm2 He ++ 2s2p He ** (2s2, 2p2) 1s2p HHG from nsec laser He(1s2) • density：1 torr • Volume： (10μm)2 x3mm • 350 events/shot • probe　(probability10-3) 480 asec, 27.2 eV, 4x1012 W/cm2

  18. T Summary • Probing molecule like motions of a 2 electron atom by asec pulses • Tomographic imaging of 2-e densities in momentum space • Coherent control • Many electron systems

  19. Control/Manipulate wavepacket • Similar idea to coherent control of molecules • Frank-Condon • Selective excitation using 2 pulses • etc Adiabatic Potential ２DOubly excited states Ground state Uμ He(1Se) Hyperradius Ｒ

  20. selective excitations Single pulse from 1s2p Double pulse from 1s2p 2p2 1De 2p2 1Se ２ｓ 2s2 1Se Ionization prob. by pump 2s2 1Se 2p2 1Se Electron energy Electron energy Ionization prob by pump-probe <θ12> Delay time Delay time

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