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Fragmentation Dynamics of H 2 + / D 2 + in Intense Ultrashort Laser Pulses

Kansas State AMO PHYSICS. Results:. initial vibr. state dependence intensity dependence pump-probe study of coherent vibr. motion. Fragmentation Dynamics of H 2 + / D 2 + in Intense Ultrashort Laser Pulses. B. Feuerstein* and U. Thumm.

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Fragmentation Dynamics of H 2 + / D 2 + in Intense Ultrashort Laser Pulses

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  1. Kansas State AMO PHYSICS • Results: initial vibr. state dependence intensity dependence pump-probe study of coherent vibr. motion Fragmentation Dynamics of H2+ / D2+ in Intense Ultrashort Laser Pulses B. Feuerstein* and U. Thumm Department of Physics, Kansas State University, Manhattan, KS, 66506, USA *Permanent address: MPI für Kernphysik, Heidelberg, Germany Outline: • Introduction • Method of Calculation

  2. Time scales Tcycle = 2.7 fs Telectr = 0.01 fs Tv=0 = 14 (20) fs Tpulse = 5 -150 fs Energies Ip = 30 eV  = 1.5 eV De = 2.8 eV Length scales l = 16000 a.u. (800 nm) R0 = 2 a.u. INTRODUCTION Laser pulse (Ti:sapphire) H2+ (D2+)

  3. H0 + H+ dissociation H+ + H+ Coulomb explosion 2 2 single ionization 3 3 4 4 1 1 dissociation fast coulomb explosion (FCE) enhanced ionization (CREI) H2 H2+

  4. 50 fs Most experiments: H2 initial state (except recent H2+ experiments: Williams et al JPB 33 (2000) 2743, Sändig et al PRL 85 (2000) 4876) Thompson et al JPB 30 (1997) 5762 Posthumus et al JPB 32 (1999) L93

  5. Dressed potential curves (schematic)

  6. Dressed potential curves (schematic)

  7. Dressed potential curves (schematic)

  8. Dissociation and Ionization paths p + p CE Charge resonance enhanced ionization (CREI) E [a.u.] H2+ Zuo, Chelkowski, Bandrauk PRA 48 (1993) 3837 u 1w g 2(3)w R [a.u.]

  9. z p p e- R METHOD OF CALCULATION Laser field 2x1D model 2D Crank-Nicholson split-operator propagation

  10. Improved soft-core Coulomb potential R-dep. softening functiona(R) + fixed shape parameter b = 5 Fixed softening parametera = 1 a(R) adjusted to (exact) 3D pot. curve (Kulander et al PRA 53 (1996) 2562) present result

  11. This work (1D) Dipole oscillator strength for sg – su transitions } Kulander et al PRA 53 (1996) 2562

  12. Array for 2x1D collinear non-BO wave packet propagation “virtual detector” method z: electron coordinate R: internuclear distance Grid: z = 0.2 a.u.; R = 0.05 a.u.

  13. Differential data: “virtual detector” Dissociation Integration over z and binning  fragment momentum distribution Coulomb explosion Integration over R and binning  fragment momentum distribution

  14. RESULTS Integrated data: time evolution of norm and fragmentation probabilities (dissociation and CE) Time evolution of probability density r(R,t) for the nuclei – CE channel is indicated by the ionization rate jz(R,t) Kinetic energy spectra of the fragments • Single pulse (I = 0.05 – 0.5 PW/cm2, 25 fs): • vibrational state and intensity dependence B)Pump-probe pulses (I = 0.3 PW/cm2, 25 fs): CE-imaging of dissociating wave packets C)Ultrashort pump-probe pulses (I = 1 PW/cm2, 5 fs): CE-imaging of bound and dissociating wave packets

  15. Coulomb explosion a - - - - - (Coulomb energy) a c b c d d b 2(3)  V 0 19 1  V 5 19 v = 4 0.2 PW/cm2 25 fs PCE(t) Dissociation PD (t) Laser Norm(t) log scale Contours: jz(R,t)

  16. Dissociation Coulomb explosion - - - - - (Coulomb energy) 2(3)  V 0 19 1  V 5 19 Norm(t) v = 0 0.2 PW/cm2 25 fs Laser PD (t) PCE(t) log scale

  17. Coulomb explosion - - - - - (Coulomb energy) 2(3)  V 0 19 1  V 5 19 v = 1 0.2 PW/cm2 25 fs Norm(t) Dissociation PD (t) Laser PCE(t) log scale Contours: jz(R,t)

  18. Dissociation Coulomb explosion - - - - - (Coulomb energy) 2(3)  V 0 19 1  V 5 19 v = 2 0.2 PW/cm2 25 fs PCE(t) PD (t) Norm(t) Laser log scale Contours: jz(R,t)

  19. Dissociation Coulomb explosion - - - - - (Coulomb energy) 2(3)  V 0 19 1  V 5 19 v = 3 0.2 PW/cm2 25 fs PCE(t) PD (t) Norm(t) Laser log scale Contours: jz(R,t)

  20. Coulomb explosion a - - - - - (Coulomb energy) a c b c d d b 2(3)  V 0 19 1  V 5 19 v = 4 0.2 PW/cm2 25 fs PCE(t) Dissociation PD (t) Laser Norm(t) log scale Contours: jz(R,t)

  21. Dissociation Coulomb explosion - - - - - (Coulomb energy) 2(3)  V 0 19 1  V 5 19 v = 5 0.2 PW/cm2 25 fs PCE(t) PD (t) Laser Norm(t) log scale Contours: jz(R,t)

  22. Dissociation Coulomb explosion - - - - - (Coulomb energy) 2(3)  V 0 19 1  V 5 19 PCE(t) v = 6 0.2 PW/cm2 25 fs PD (t) Laser Norm(t) log scale Contours: jz(R,t)

  23. Dissociation Coulomb explosion - - - - - (Coulomb energy) 2(3)  V 0 19 1  V 5 19 PCE(t) v = 7 0.2 PW/cm2 25 fs PD (t) Laser Norm(t) log scale Contours: jz(R,t)

  24. Dissociation Coulomb explosion - - - - - (Coulomb energy) 2(3)  V 0 19 1  V 5 19 PCE(t) v = 8 0.2 PW/cm2 25 fs Laser PD (t) Norm(t) log scale Contours: jz(R,t)

  25. 0.1 PW/cm2 0.1 PW/cm2 0.05 PW/cm2 0.05 PW/cm2 2 2 2 2 1 1 1 1 0.2 PW/cm2 0.2 PW/cm2 0.5 PW/cm2 0.5 PW/cm2 2 2 2 2 1 1 1 1 0w 1w 2w 3w v = 3 v = 6

  26. 2(3)  CE 1  Pump-probe experiment D2 target 0.1 PW/cm2 2 x 80 fs variable delay 0 - 300 fs Trump, Rottke and Sandner PRA 59 (1999) 2858

  27. b c a c b a Pump-probe (D2+) v = 0 0.3 PW/cm2 2 x 25 fs delay 30 fs Norm(t) PCE(t) Dissociation Coulomb explosion Laser PD (t) - - - - - (Coulomb only) log scale Contours: jz(R,t)

  28. Pump-probe (D2+) v = 0 0.3 PW/cm2 2 x 25 fs delay 50 fs Norm(t) PCE(t) Dissociation Coulomb explosion PD (t) Laser - - - - - (Coulomb only) b c a log scale Contours: jz(R,t) c b a

  29. Pump-probe (D2+) v = 0 0.3 PW/cm2 2 x 25 fs delay 70 fs Norm(t) PCE(t) Dissociation Coulomb explosion Laser PD (t) - - - - - (Coulomb only) b c a log scale Contours: jz(R,t) c b a

  30. Time evolution of a coherent superposition of states Time dependent density matrix: Time average: Incoherent mixture H2+ (wkm-1 = 3 … 30 fs): produced by: Ion source: T ms  incoherent ensemble Ultrashort laser pulse: T  5 fs  coherence effects expected

  31. D0 + D+ H+ + H+ t probe 2 PW/cm2 5 fs autocorrelation D2+ D2 pump 1 PW/cm2 5 fs

  32. Kinetic energy Ekin (R) Coulomb explosion imaging of nuclear wave packets Fragment yield Y at Ekin: Y(Ekin) dEkin= |(R)|2 dR Y(Ekin) = R2|(R)|2 1/R d + d Probe |(R,t)|2 R D2+ Pump D2 initial |(R)|2

  33. reconstructed |(R)|2  = 10 fs original |(R)|2 |(R)|2 incoherent FC distr. |(R)|2reconstruction from CE fragment kin. energy spectra moving wave packet

  34. reconstructed |(R)|2  = 20 fs original |(R)|2 incoherent FC distr. |(R)|2 |(R)|2reconstruction from CE fragment kin. energy spectra turning point

  35. reconstructed |(R)|2  = 30 fs original |(R)|2 incoherent FC distr. |(R)|2 |(R)|2reconstruction from CE fragment kin. energy spectra

  36. reconstructed |(R)|2 original |(R)|2 incoherent FC distr. |(R)|2reconstruction from CE fragment kin. energy spectra  = 40 fs |(R)|2

  37. reconstructed |(R)|2 original |(R)|2 incoherent FC distr. |(R)|2reconstruction from CE fragment kin. energy spectra  = 165 fs |(R)|2 ‘collapse’

  38. reconstructed |(R)|2  = 580 fs original |(R)|2 incoherent FC distr. |(R)|2 |(R)|2reconstruction from CE fragment kin. energy spectra ‘revival’

  39. WHAT’S NEXT ? Thumm Group: • More on time-resolved nuclear dynamics: • decoherence and revivals • Add degrees of freedom: 2D (electron) + 1D(R) • H2: 2 x 1D (electrons) + 1D(R) • Lasser-assisted collisions B.F.: GOES BACK TO EXPERIMENT! (Good Bye, Theory)

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