1. Photoelectron diffraction from small molecules:
Structure and Dynamics of Atoms, Ions, Molecules and Surfaces: Atomic Physics with Ion Beams, Lasers and Synchrotron Radiation 2004 Research Meeting of the BES AMOS Program
C.L.Cocke, Physics Department, J.R. Macdonald Laboratory, Kansas State University, Manhattan, KS
Current Projects:
Multiple electron removal from neutral systems studied with COLTRIMS (Cocke, Lin, Tong, Chang..)
Photoelectron diffraction from small molecules:
a) ALS: Synchrotron radiation (Many..)
b) KSU: Harmonic generation source, time-resolved studies (Cocke,Chang,Shan…)
3) Picopulsing the Tandem (Chang,Carnes,Cocke,Needham,Richard,DePaola,Ben Itzhak, ..)
Konza prairie just outside Manhattan

2. Mechanisms for Double Electron Removal from Light Molecules by Intense Laser Pulses: Fast Clocks
The time line in seconds:
10-12
10-18
10-15
10-9
Phase transitions
Electronic motion
Heavy particle motion
Radiative lifetimes
Collisions: integrated trajectories
Attosecond pulses
Pulsed Lasers: real time movies

3. Electron rescattering from molecules in intense laser fields
Ali Alnaser, S.Voss, T.Osipov, M.Benis, B.Ulrich, C.Maharjan,
X.-M.Tong, C.D.Lin, Z.Chang, B.Shan,P.Ranitovic,C.L.Cocke
D2/H2
Old and new mechanisms for double electron removal
and fs clocks
N2/O2
Mechanisms for double electron removal:
Does the orbital structure play a role and how?
Tuttle creek reservoir just outside Manhattan

4. Experimental setup: COLTRIMS
Laser
supersonic Jet X Y Z
E-Field
Recoil Detector
Spectrometer
Time resolution: <1 ns
Position resolution: 0.3 mm
Multihit: 16 events/pulse
Pulse pair resolution: 15 ns
B field gauss
E field 1-10 V/cm
Flight distances cm
Vacuum < torr
Ion detection only
Intensity : x1014 Watt/cm2
800 nm Wavelength
1-2 kHz Repetition Rate
8-35 fs

5. The COLTRIMS apparatus with an operator….
Predrag Ranitovic

6. The other apparatus with operators
M.Zamkov C.Wang M.Benis S.Voss L.Cocke A.Alnaser
T.Osipov B.Shan C.Maharjan

7. Electron rescattering from molecules in intense laser fields
Ali Alnaser, S.Voss, T.Osipov, M.Benis, B.Ulrich, C.Maharjan,
X.-M.Tong, C.D.Lin, Z.Chang, B.Shan, C.L.Cocke
D2/H2
Old and new mechanisms for double electron removal
and fs clocks
N2/O2
Mechanisms for double electron removal:
How do you get the electronic energy into the system?
Does the orbital structure play a role and how?

8. The hydrogen (deuterium) molecule
The Kinetic Energy Release spectra
Background
Dissociation
Double ionization: enhanced ionization
Rescattering
Sequential Ionization
Clocking the wave packet on a fs time scale using all three processes
Konza prairie just outside Manhattan

9. d+ time of flight spectrum along laser polarization

10. The data: p+ or d+ spectra
Frazinski et al, PRL 83, 3625
A.Zavriyev et al.,PRA 42, 5500 (1990).
H+ + H+ BS
CREI
ATD
H+ + H
H + H

11. d+ time of flight spectrum along laser polarization

12. Rescattering:the electron returns with energy
-Maximum return energy
3.17 Up at phase of 17 degrees
-If circularly polarize the light,
electron does not return

13. Staudte et al.:the energy distributions of coincident ion pairs d+/d+
???
A.Staudte, C.L.Cocke, M.H.Prior et al., Phys.Rev.A 65, (R) (2002)
CREI

14. Niikura et al., Nature 417,917 (2002)

15. Mechanisms for doubly ionizing H2
Rescattering
Enhanced
H. Niikura, et. al., Nature 417, 917 (2002); Nature 421, 826 (2003).
Seideman et al., PRL 75, 2819 (1995);Zuo and Bandrauk, PRA 52, R2511 (1995).
Increasing intensity
Increasing intensity

16. How we identify rescattering in the double ionization channel: linear/circular polarization
Linear Polarization
Circular Polarization
|p1+p2|
A. Staudte et al, , PRA 65, R (2002)
A. Alnaser, et al., PRL 91, (2003)
Magnitude of vector sum of momentum of two fragments

17. General character of results
cos(q)
Ion sum energy (eV) 1 -1 20
1.1
2.5
1.6
1.3
1.2
1.5
Spectra at various peak laser intensities
(in units of w/cm2 )
CREI
Rescattering q e

18. The model X.M.Tong, Z.X.Zhao and C.D.Lin, PRA 68, 043412 (2003) ADK
Classical electrons
Theoretical differential
excitation cross sections
Vibrational wave
packet propagation
ADK

19. Multiple returns: the 2.7 fs clock
A. Alnaser, et al., PRL 91, (2003)
Return
Time ( fs)
<R>( a.u.)
H2+
D2+ t1
1.9
1.8
1.6 t3
4.3
2.5
2.1 t5
7.0
3.0
2.6 t7
9.6
3.2
35 fs, 2.8 x w/cm2
* Model by X.M.Tong, Z.X.Zhao and C.D.Lin, PRA 68, (2003)

20. The short pulse: 8 fs
In rescattering regime, can isolate first return.

21. The short pulse: only the first return
The short pulse: 8 fs, 1.5 x W/cm2

22. The hydrogen (deuterium) molecule
The Kinetic Energy Release spectra
Background
Dissociation
Double ionization: enhanced ionization
Rescattering
Sequential Ionization
Clocking the wave packet on a fs time scale using all three processes

23. Sequential ionization in non-coincident data with short pulse
Légaré et al., PRL 91, (2003)

24. Mechanisms for doubly ionizing H2
Rescattering
Enhanced
Sequential
H. Niikura, et. al., Nature 417, 917 (2002); Nature 421, 826 (2003).
Seideman et al., PRL 75, 2819 (1995);Zuo and Bandrauk, PRA 52, R2511 (1995).
Légaré et al., PRL 91, (2003)
Increasing intensity
Increasing intensity

25. The hydrogen (deuterium) molecule
The Kinetic Energy Release spectra
Background
Dissociation
Double ionization: enhanced ionization
Rescattering
Sequential Ionization
Clocking the wave packet on a fs time scale using all three processes

26. The shortish pulse spectrum: all three processes
time direction
Momentum slice in plane containing polarization vector of internal motion of proton pair
12 fs, 2 x w/cm2

27. Model and Experiment Model: Expt: Alnaser et al. Tong, Lin and Zhao
10 fs, 4 x w/cm2
12 fs, 2 x w/cm2

28. Overview of ionization and vibrational wave packet center
Model:
Tong, Lin and Zhao
10 fs, 4 x w/cm2

29. Electron rescattering from molecules in intense laser fields
Ali Alnaser, S.Voss, T.Osipov, M.Benis, B.Ulrich, C.Maharjan,
X.-M.Tong, C.D.Lin, Z.Chang, B.Shan, P.Ranitovic, C.L.Cocke
D2/H2
Old and new mechanisms for double electron removal
and fs clocks
N2/O2
Mechanisms for double electron removal:
How do you get the electronic energy into the system?
Does the orbital structure play a role and how?

30. Coulomb imaging used to take snapshots of molecule?
How does snapshot really go and how long does it last?
O2+4
O2+3
O2+2
O2+ O2

31. N2 and O2 :Are there similar mechanisms for heavier molecules?
Rescattering
Enhanced
Sequential/MP O2
O2+
O2+2 TI TI TI
O2+2
O2+2
O2+2
O2+2 MP MP
O2+
O2+
O2+
O2+ TI TI O2 O2 O2 O2
Yes, but not with
Short pulses
Not without MP
step
Yes
Low intensity, < 2x w/cm2
High intensity, >5x10 14 w/cm2

32. Time of flight spectra for oxygen

33. Rescattering region (below 2 x 10 14 w/cm2): the momentum spheres have fine structure: oxygenz e q

34. O22+ 3sg -1pg-1 O2 pu -1pg-1 ..3sg2 pu4 pg2
The states populated are the same as are known from electron scattering
pu -1pg-1
3sg -1pg-1
O22+ O2
..3sg2 pu4 pg2
M. Lundqvist et al., J.Phys.B 29
499 (1996)
Electrons
Kinetic Energy Release (eV)
Laser
Kinetic Energy Release(eV)

35. The process… O2
O2+
O2+2 TI e-
P1(q)
P3(q)
P2(q)

36. Angular distributions of N2 and O2
Can the alignment dependence of the first step , the production of the singly charged molecule, be seen? For H2, this distribution was isotropic; for other molecules, it is predicted by molecular ADK to reflect orbital structure. O+ - N+ + + e
N pu4 3sg2
O sg2 pu4 pg2

37. Momentum slices of N2 and O2 in rescattering region (short pulse)
Pairs of singly charged ions only

38. The polar plots…
pu -1pg-1

39. Molecular ADK Model 1.5 x 1014 watt/cm2, 8fs Model Experiment
X. M. Tong, Z. X. Zhao, and C. D. Lin, Phys.Rev.A, 66, (2002)

40. Summary :
For the hydrogen molecule, the vibrational molecule wave packet can be tracked on fs time scale using the optical cycle (2.7 fs) as a clock. This works when the double ionization is driven by rescattering or sequential ionization (not enhanced ionization).
For nitrogen and oxygen, in the rescattering region, the expansion is initiated through population of well defined states of the dication (Coulomb potentials are irrelevant).
The structure of the outermost orbitals is seen in the alignment dependence of the double ionization and supports the molecular ADK prediction.

41. Other issues:
The dynamic alignment (a posteriori) of molecules/fragments
Bond-softening couplings which peak at 90 degrees
The short pulse “freezes” the nuclear motion

42. p g removal : short pulse
1.5 3
Intensities in w/cm2
8 fs pulse 7 8

43. O2 short pulse KER vs angle
KER (eV) q O+
Cos (q)

44. Future plans
Do the orbital mappings apply to other systems?

45. Other systems.. C2H2 CO2 CO pu pg s Theory
Preliminary experiment (lowest intensity)

46. Future plans Do the orbital mappings apply to other systems?
Pump-probe experiments:
Can the vibrational wave function be mapped out as a function of time?

47. Future plans: pump-probe
Oscillation of wave packet in 1sg potential
Sequential
D+ + D+
Field Ionization probe, strong
D2+
Time delay t
Field Ionization pump, weak D 2
Enhanced ionization
First results for molecular hydrogen
Increasing intensity

48. Future plans Do the orbital mappings apply to other systems?
Pump-probe experiments:
Can the vibrational wave function be mapped out as a function of time?
Use of electrons as “second hand” of clock

49. THE END