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

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Structure and Dynamics of Atoms, Ions, Molecules
and SurfacesAtomic Physics with Ion Beams,
Lasers and Synchrotron Radiation2004 Research
Meeting of the BES AMOS Program
C.L.Cocke, Physics Department, J.R. Macdonald
Laboratory, Kansas State University, Manhattan,
KS 66506

• 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,Ne
  edham,Richard,DePaola,Ben Itzhak, ..)

Konza prairie just outside Manhattan
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Mechanisms for Double Electron Removal from Light
Molecules by Intense Laser Pulses Fast Clocks
The time line in seconds
10-12
10-15
10-9
10-18
Phase transitions
Radiative lifetimes
Heavy particle motion
Electronic motion
Collisions integrated trajectories
Attosecond pulses
Pulsed Lasers real time movies
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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
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Experimental setup COLTRIMS
Laser
Time resolution lt1 ns Position resolution 0.3
mm Multihit 16 events/pulse Pulse pair
resolution 15 ns B field 10-20 gauss E field
1-10 V/cm Flight distances 10-50 cm Vacuum lt 10
-10 torr
Ion detection only
Intensity 0.9 -8 x1014 Watt/cm2 800 nm
Wavelength 1-2 kHz Repetition Rate 8-35 fs
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The COLTRIMS apparatus with an operator.
Predrag Ranitovic
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The other apparatus with operators
M.Zamkov C.Wang M.Benis S.Voss L.Cocke
A.Alnaser T.Osipov B.Shan
C.Maharjan
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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?
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The hydrogen (deuterium) molecule
The Kinetic Energy Release spectra Background Di
ssociation 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
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d time of flight spectrum along laser
polarization
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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
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d time of flight spectrum along laser
polarization
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Rescatteringthe electron returns with energy
-Maximum return energy 3.17 Up at phase of 17
degrees -If circularly polarize the
light, electron does not return
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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, 020703 (R) (2002)
CREI
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Niikura et al., Nature 417,917 (2002)
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Mechanisms for doubly ionizing H2
Rescattering
Enhanced
Seideman et al., PRL 75, 2819 (1995)Zuo and
Bandrauk, PRA 52, R2511 (1995).
H. Niikura, et. al., Nature 417, 917 (2002)
Nature 421, 826 (2003).
Increasing intensity
Increasing intensity
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How we identify rescattering in the double
ionization channel linear/circular polarization
A. Staudte et al, , PRA 65,020703 R (2002) A.
Alnaser, et al., PRL 91, 163002 (2003)
Magnitude of vector sum of momentum of two
fragments
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General character of results
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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
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Multiple returns the 2.7 fs clock
A. Alnaser, et al., PRL 91, 163002 (2003)
Return Time ( fs) ltRgt( a.u.) ltRgt( 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 3.0
35 fs, 2.8 x 10 14 w/cm2
Model by X.M.Tong, Z.X.Zhao and C.D.Lin, PRA
68, 043412 (2003)
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The short pulse 8 fs

• In rescattering regime, can isolate first return.

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The short pulse only the first return
e
The short pulse 8 fs, 1.5 x 10 14 W/cm2
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The hydrogen (deuterium) molecule
The Kinetic Energy Release spectra Background Di
ssociation Double ionization enhanced
ionization Rescattering Sequential
Ionization Clocking the wave packet on a fs time
scale using all three processes
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Sequential ionization in non-coincident data with
short pulse
Légaré et al., PRL 91, 093002 (2003)
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Mechanisms for doubly ionizing H2
Rescattering
Enhanced
Sequential
Seideman et al., PRL 75, 2819 (1995)Zuo and
Bandrauk, PRA 52, R2511 (1995).
H. Niikura, et. al., Nature 417, 917 (2002)
Nature 421, 826 (2003).
Légaré et al., PRL 91, 093002 (2003)
Increasing intensity
Increasing intensity
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The hydrogen (deuterium) molecule
The Kinetic Energy Release spectra Background Di
ssociation Double ionization enhanced
ionization Rescattering Sequential
Ionization Clocking the wave packet on a fs time
scale using all three processes
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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 10 14 w/cm2
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Model and Experiment
Model Tong, Lin and Zhao
Expt Alnaser et al.
12 fs, 2 x 10 14 w/cm2
10 fs, 4 x 10 14 w/cm2
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Overview of ionization and vibrational wave
packet center
Model Tong, Lin and Zhao
10 fs, 4 x 10 14 w/cm2
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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?
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Coulomb imaging used to take snapshots of
molecule?
O25
How does snapshot really go and how long does it
last?
O24
O23
O22
O2
O2
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N2 and O2 Are there similar mechanisms for
heavier molecules?
Enhanced
Rescattering
Sequential/MP
TI
TI
O22
O22
O22
O22
MP
MP
O2
O2
O2
O2
TI
TI
O2
O2
O2
O2
Not without MP step
Yes, but not with Short pulses
Yes
Low intensity, lt 2x 10 14 w/cm2
High intensity, gt5x10 14 w/cm2
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Time of flight spectra for oxygen
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Rescattering region (below 2 x 10 14 w/cm2) the
momentum spheres have fine structure oxygen
q
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The states populated are the same as are known
from electron scattering
O2 ..3sg2 pu4 pg2
M. Lundqvist et al., J.Phys.B 29 499 (1996)
Electrons
Kinetic Energy Release (eV)
Laser
Kinetic Energy Release(eV)
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The process
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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
O2 ..3sg2 pu4 pg2
N2 .. pu4 3sg2
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Momentum slices of N2 and O2 in rescattering
region(short pulse)
Pairs of singly charged ions only
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The polar plots
pu -1pg-1
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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, 033402 (2002)
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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.
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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
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p g removal short pulse
1.5
3
Intensities in 10 14 w/cm2 8 fs pulse
7
8
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O2 short pulse KER vs angle
O
e
q
KER (eV)
O
Cos (q)
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Future plans

• Do the orbital mappings apply to other systems?

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

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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
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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

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THE END