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

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

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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 vibrational state dependence intensity dependence pump-probe study of coherent vibrational motion Fragmentation Dynamics of H2+ / D2+ in Intense Ultrashort Laser Pulses U. Thumm B. Feuerstein T. Niederhausen Kansas State University • Introduction • Method of Calculation

  2. Laser pulse (Ti:sapphire) H2+ (D2+) 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

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

  4. weak field 0w p + p 1w CE 2w 3w Charge resonance enhanced ionization strong field E [a.u.] 0w H2+ u 1w 1w g 2w 2(3)w 3w Dressed potential curves (schematic) R [a.u.] Dissociation and Ionization paths

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

  6. 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 Improved soft-core Coulomb potential

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

  8. 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.

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

  10. RESULTS Time evolution of wave function and norm (on numerical grid) Evolution of nuclear probability density r(R,t ) dissociation probability ionization ratejz(R,t) CE probability 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

  11. 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) total fragment energy [eV] log scale Contours: jz(R,t)

  12. 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

  13. 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)

  14. 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)

  15. 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)

  16. 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)

  17. Branching ratio : Dissociation vs. Coulomb explosion

  18. RESULTS II • 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

  19. 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

  20. 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)

  21. 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

  22. 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

  23. RESULTS III • 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

  24. 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 Time evolution of a coherent superposition of states

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

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

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

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

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

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

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