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Investigating Time Correlation of Sequential Electron Release by Short Laser Pulses

Explore electronic dynamics at sub-fs scale by measuring the time correlation of two electrons released from atomic targets using short laser pulses. Full vector momentum of ions and electrons is measured to map electron momenta. Investigate momentum conservation and angular correlation between emitted electrons. Address random electron counts and false coincidences.

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Investigating Time Correlation of Sequential Electron Release by Short Laser Pulses

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  1. Correlation in theSequential Release Of Two Electrons from Atomic Targets by Short Laser Pulses Chakra Man Maharjan Collaborators: A. S. Alnaser, X. M. Tong, P. Ranitiovic, I. Litvinuyk, and C.L. Cocke

  2. Basic Concept ……………… e1- Ar2+ Ar e2- Fraction of an optical period E ωt Sub femto-second Electrons dynamics Optical period=2.6 fs

  3. OUTLINE The Goal: to directly measure the time correlation between the two electrons and explore the clock that reads electronic dynamics of the system on sub-fs scale • Tool : Measure in COINCIDENCE the highly resolved momentum distributions of electrons and doubly-charged ions produced in the circularly polarized ultra short laser pulse. • What is achieved : the full vector momentum of the singly and doubly charged recoil ions (Ar and Ne) is measured. The ion momentum distributions can also be used to map the vector sum of the two emitted electrons’ momenta.

  4. Sequential ionization Mechanism???? Tunneling Ionization At high laser intensities; Over barrier ionization E=Ip2/4Zeff P =E/ω

  5. How electrons and ion gain momentum in laser field? Momentum conservation……….

  6. How P1 and P2 related to E at time of release E=E0 e-t2/T2 (x Sinwt+ y Coswt) Linearly polarized pulse Circularly Polarized pulse E P2 P1 For Ar Electric field for over the barrier Ar : 0.0841 a.u. (Io=4.95x1014W/cm2) Ar+:0.1287 a.u. (Io= 1.16 x1015 W/cm2) P=E(t)/ω

  7. The second hand clock!! Angular correlation between two electrons P1 Φ E1 Φ= cos-1(P1.P2/|p1||p2|) E2 P1=E1/ω P2 P2=E2/ω Time correlation ωt t= Φ/ω Phase stabilized laser……….

  8. Experimental setup (COLTRIMS) Mirror Y e detector Ion Detector qn+ Z e- Laser X Magnetic coil Measure: Time and position JET B

  9. Measure t, x, y Px, Py, Pz, Energy, angle Calculate Electron raw data( time of flight) Counts Tof (ns)

  10. Wiggles Spectrum Calibration of parameters used in the experiment r(0.5 mm) Tc TOF(ns) Cyclotron Period Px=mωc (X cot(ωctof/2)+Y)/2 Py=mωc (Y cot(ωctof/2)-X)/2

  11. Distribution of electrons in the plane perpendicular to the direction of the laser propagation Y Po Eo=Pω Io=cЄoEo2 X Io=4x1014 W/cm2 Z PD~ 8 fs

  12. Ions’ Tofs and positions Io=1.8x1015 W/cm2 PD = 8 fs Ar+ Ar2+ Time of Flight O2+ Background Position Image Target (jet)

  13. Ar+ Ar2+ Io=1.8x1015 W/cm2 PD = 8 fs Single and Double Ionization of Ar Target ( Circular Polarization)

  14. e e Ar2+ Ar2+ Ar1+ Ar1+ e e e Ar1+ Ar2+ Ar1+ e e e e e e e e e e e Ar1+ Ar1+ e Ar2+ e Ar1+ e Ar2+ e Ar1+ Z Zo Big Problem……. Random electron counts

  15. True coincidence Detector e Ar2+ e

  16. False coincidence Detector e Ar2+ Ar1+ e Ar1+ e e Two ways to decrease random counts 1.Decrease counts rate 2.Decrease the size of target beam

  17. Use piezoelectrical slits to minimize Volume effects 1 0 -1 jet spherical mirror laser manipulator laser focus

  18. pzr Pze1 Double Coincidence Conservation of momentum !!!! FWHM=0.43a.u Pze1+Pzr Io=4x1014 W/cm2 PD = 8 fs

  19. Triple coincidence Pzr Pze1+Pze2+Pzr Pze1+Pze2 Io=1.8x1015 W/cm2

  20. How are these spectra related to the correlation between two electrons ? Model by:X.M.Tong & C.D.Lin Ar2+ momentum spectra

  21. Ion momentum distribution reflects the vector sum of momenta of two electrons Model by:X.M.Tong & C.D.Lin Ne2+ momentum spectrum

  22. The sum momentum spectrum:Ne as test case p1 p2 Ne++ Ne+ Counts pz

  23. Momentum of electrons at the over barrier………. Ar2+ Ar2+ Ne2+ P1+P2 P1-P2 Ne2+ P1+P2 P1-P2

  24. Momentum distribution of Ne2+ and Ar2+ in the polarization plane P1+P2 P1-P2 Ne2+ Ar2+ (Io=1x1016 W/cm2) (Io=4.5x1015 W/cm2)

  25. At the end…… 1.Random (false) counts is the main problem to investigate the time correlation between two electrons emitted sequentially with coincident technique. 2.we are pretty much successful to get angular correlation of two electrons using the doubly charged ion momentum spectra

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