Dissociative Ionization of N2 in an Ultrafast Strong Field

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Queens University Belfast
J McKenna M Suresh B Srigengan I D Williams
Dissociative Ionization of N2 in an Ultrafast
Strong Field
University College London
J Wood E M L English S L Watson W A Bryan W R
Newell
Jarlath McKenna
Rutherford Appleton Laboratory
I C E Turco J Smith E Divall C J Hooker A
Langley J Collier
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Whats coming up??
Very Brief Overview of Experimental Setup
Intensity Selective Scan technique
Single and Double Ionization of N2
Linear-Circular comparison.
Role of Alignment Rescattering effects.
Dissociation of N2 via (1,0) channel
Kinetic energy release from MEDI of N2
Comparison at 55 fs and 220 fs pulse duration
Modelled using Classical Trajectory calculations
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Time-of-Flight Mass Spectrometer.
ASTRA Target Area 1
50-55 fs pulse duration
20 mJ per pulse
10 Hz repetition rate
gt 6x1016 Wcm-2 peak intensity
Wiley-McLaren Conditions
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Time-of-Flight Mass Spectrometer.
Intensity Selective Scan
Wiley-McLaren Conditions
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Time-of-Flight Mass Spectrometer.
Intensity Selective Scan
Wiley-McLaren Conditions
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Time-of-Flight Mass Spectrometer.
Intensity Selective Scan
Wiley-McLaren Conditions
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Time-of-Flight Mass Spectrometer.
Intensity Selective Scan
Wiley-McLaren Conditions
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Single Ionization of N2.
N2
N2 laser ? N2 e-
LinearCircular Intensity Ratio
0.65
M Suresh et al. CLF Annual Report 2003-2004
pp67-69
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Single Ionization of N2.
N2
Dynamic Alignment
LinearCircular Intensity Ratio
0.65
M Suresh et al. CLF Annual Report 2003-2004
pp67-69
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Single Ionization of N2.
?
?cos?

N2
Geometric Alignment
?
-
LinearCircular Intensity Ratio
0.65
M Suresh et al. CLF Annual Report 2003-2004
pp67-69
11
How about double ionization?
N22
Strong enhancement with linear polarization
Nonsequential ionization
-rescattering
Alignment enhanced rate
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Comparison to atomic counterpart, Ar
N22
Similar first ionization potentials
Ar 15.76 eV
N2 15.58 eV
Ar2
Nonsequential Ionization apparent for Ar2
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Bond-softening dissociation of N2
Observed in the N (1,0) dissociation channel
KER 0.9 eV
(1,0)
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Enhanced linear dissociation of N2 !!
N (1,0)
KER 0.9 eV
? Full collection efficiency for both
polarizations
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N (1,0)
Nonsequential dissociation of CO2
CO2 ? CO O
CO
Rescattering is a low intensity effect
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N
Multielectron Dissociative Ionization (MEDI) of
N2
Experiment
N2
- SI units
Calculated
N3
- KER in eV, q in au, Re in Å
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KER via Coulomb Explosion channels
Determined with Linear Polarization (I 1.5x1016
Wcm-2)
.dissociation at Re 2.08 a.u.
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KER via Coulomb Explosion channels
Up to (3,3) channel, experimental KER is approx.
half that from Coulomb explosion at Re
0.5
KER from 220 fs is slightly lower than for 55 fs
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KER via Coulomb Explosion channels
0.5
Experimental / (Calculation at Re)
N4 and N5 ions appear with energies much lower
than general trend
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Posthumus et al J. Phys. B, 29, 5811 (1996)
Classical Appearance Intensities
N2 (1,1)
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Classical Appearance Intensities
(1,1) channel
Rc 7 a.u.
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and now the Classical Trajectories
(1,0)
220fs, 8x1014 Wcm-2
55fs, 8x1014 Wcm-2
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and now the Classical Trajectories
(1,1)
220fs, 8x1014 Wcm-2
55fs, 8x1014 Wcm-2
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and now the Classical Trajectories
(1,2)
220fs, 8x1014 Wcm-2
55fs, 8x1014 Wcm-2
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and now the Classical Trajectories
(2,2)
220fs, 8x1014 Wcm-2
55fs, 8x1014 Wcm-2
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and now the Classical Trajectories
(2,3)
220fs, 8x1014 Wcm-2
55fs, 8x1014 Wcm-2
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and now the Classical Trajectories
(3,3)
220fs, 8x1014 Wcm-2
55fs, 8x1014 Wcm-2
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and now the Classical Trajectories
55fs, 8x1014 Wcm-2
Expt 28.9eV
(3,3)
Traj 28.0eV
220fs, 8x1014 Wcm-2
Expt 12.8 eV
(2,3)
Traj 11.4eV
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Post-Dissociative Ionization!!
55fs, 1.5x1016 Wcm-2
Expt 43.1eV
(5,5)
Traj 48.0eV
- PDI of (3,4)
220fs, 1.5x1016 Wcm-2
Expt 27.7 eV
(5,5)
Traj 26.5 eV
- PDI of (3,3)
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Across all channels
55 fs
Trends are reproduced well
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Across all channels
220 fs
Trends are reproduced well
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Thank-You
Happy Christmas!!!
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Across all channels
220 fs
Trends are reproduced well
Except (3,3) channel!!!
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Across all channels
220 fs
In the case of (3,3), the channel crossing point
is critical to the final KER observed
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Thank-You
Happy Christmas!!!
(Happy Holidays!!!)
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(No Transcript)
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Covariance Mapping
L J Frasinski et al., Phys. Lett. A 142, 499
(1989)
OCS
For a diatomic
where C2(t1,t2) is the ion-ion covariance, A and
B are the ion signals at all various times, and k
is each laser shot
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Collection efficiency corrections
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KER via Coulomb Explosion channels
Up to (3,3) channel, experimental KER is approx.
half that from Coulomb explosion at Re
KER from 220 fs is slightly lower than for 55 fs
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How about the (4,4) and (5,5) channels??
N4 and N5 ions appear with energies much lower
than general trend