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atomic

VIEWS: 27 PAGES: 9

									      Results using atomic targets

• Suppression of Nonsequential ionization from an atomic ion
target (comparison of double ionization of Ar and Ar+).

• Determination of intensity ratio factor for comparison of
linear to circular polarization.

• Linear-Circular comparisons of nonsequential ionization
of Xe using the intensity selective scanning technique.

• Strong field ionization of C+ ions – observation of forbidden
transition from metastable state.
   ISS results for Ar+ ion beam….

• Using the Intensity Selective Scan
                                                   Groundstate
(ISS) technique (see Experimental
Setup presentation) Ar2+ production
                                                                    Metastable
from an Ar+ ion beam is measured as a
function of focusing lens position.
• The large peak at z=0mm results from
ionization of groundstate Ar+ ions
requiring the strongest field (highest
intensity).

• The two peaks either side of zero
position are due to metastable Ar+ ions
(lower IP) displaying the expected
profile resulting from the interplay of     Ar2+ production from Ar+ ion beam
increasing interaction volume with            (a) 1016 Wcm-2
decreasing intensity as the lens moves        (b) 5  1016 Wcm-2
away from zero.

• The groundstate peak at z = 0 therefore disappears rapidly compared to the
metastable peaks at z = ±12 as the intensity decreases.
   Suppression of Nonsequential component….


 Comparison of double ionization
 from Ar+ ionic target and Ar neutral
 target



  Ratio of Ar3+ to Ar2+ production

 • Neutral target  0.038 ± 0.002
 • Ionic target  0.007 ± 0.002


  Multiple ionization of ionic target is
  strongly suppressed!


For more info, see publication:            TOF spectra (similar conditions) for
  J. B. Greenwood et al                    (a) neutral Ar and (b) Ar+ beam
  Phys. Rev. Lett. 88. 233001 (2002)       Note: (b) (i) Ar2+ and (ii) Ar3+ (x 50 vertical scale)
   Comparison of Linear – Circular Polarization….
For a quantitative comparison of linear-circular nonsequential contribution,
need to match the sequential ionization components.

As linear polarization is an oscillating field but circular is constant in amplitude,
it’s not suffice to simply match the peak E-field amplitude. We need to match
the time-averaged tunnel rates over the period of a laser cycle.

                                                                    ADK curves for Xe (circular intensity scaled x1.3)
From ADK tunneling theory,
                                                                   1010
Linear rate 1.3E0  Circular rate E0
                                                                   109        Linear I
                                                                              Circular 1.3*I
                                                                                                      Xe+



                                           Ion Yield (arbitrary)
                                                                   108                                        Xe2+
                                                                               g = 0.5
For Circular field E0/ 2 (intensity I),                           107
                                                                                               1010

                                                                   106                         109

matching Linear field is 1.3 x (E0/ 2)                                                       108

                                                                   105                         107

    i.e. 0.81E0 (intensity 0.65I)                                                              106

                                                                   104                         105

                                                                                               104
                                                                                                                     Unshifted
                                                                   103                         103

    Circular              Linear                                                               102
                                                                                                       1014   1015      1016     1017
                                                                   102
   Intensity I        Intensity 0.65I                                         1014             1015             1016               1017
                                                                                         Intensity (Wcm-2)
Experimental verification of intensity ratio of 0.65….

                                                                                               Linear                   Circular
                                                                               1.0




                                                 Integrated Ion Yield (arb.)
 We experimentally verified the linear-                                        0.8
                                                                                          Ne+
 circular intensity ratio of 0.65 by
                                                                               0.6
 performing an ISS on Ne gas in the
 neutral gas target apparatus                                                  0.4

                                                                               0.2

                                                                               0.0
 Ne was a good test gas to use as previous                                           -8   -6    -4      -2   0    2     4   6      8

 observations have found suppressed                                                                   Z Position (mm)




                                               Integrated Ion Yield (arb.)
                                                                               1.0
 Nonsequential double ionization from this                                                Ne2+
                                                                               0.8
 target (Becker and Faisel J. Phys. B 32
 L335 (1999))                                                                  0.6

                                                                               0.4

 The results show excellent matching of                                        0.2
 the linear and circular yields for single
                                                                               0.0
 and double ionization of Ne using the                                               -8   -6   -4      -2    0   2      4   6      8
 factor of 0.65.                                                                                     Z Position (mm)

                                             ISS for single and double ionization of Ne
ISS results from Xe neutral target (linear polarization)….




                                                     Signal (arb.)
   Time of Flight (sec)




                                              Xe+
                                                                                      129Xe2+
                                                                                      131Xe2+
                                                                                      132Xe2+




                                              Xe8+

                                                                     Temporally resolved
                                                                     isotopes of Xe2+

                          Z Position (arb.)
                                                                                  Circular            Linear
 Linear-Circular ISS results                                          1.0


 for Xe and Xe+….                                                     0.8

                                                                      0.6
                                                                                                                Xe  Xe+
                                                                      0.4

                                                                      0.2

   Loss of linear flux in Xe+                                         0.0
                                                                            -15    -10   -5   0   5   10   15

   appears as an enhanced linear                                      1.0


   signal in higher charge states




                                        Integrated Ion Yield (arb.)
                                                                      0.8

                                                                      0.6

                                                                      0.4                                       Xe  Xe2+
  Large enhancement of linear                                         0.2

                                                                      0.0
  signal in the low intensity regions                                       -15    -10   -5   0   5   10   15


  is due to the Nonsequential                                         1.0

                                                                      0.8
  ionization!                                                         0.6

                                                                      0.4
                                                                                                                Xe  Xe3+
                                                                      0.2

  Suppressed Nonsequential                                            0.0
                                                                            -15    -10   -5   0   5   10   15

  component from the ionic target                                     1.0


  as was the case for Ar also!                                        0.8

                                                                      0.6

                                                                      0.4                                       Xe+  Xe3+
For more information see :                                            0.2

                                                                      0.0
  M. Suresh et al.                                                          -15   -10    -5   0   5   10   15

  RAL Annual Report 2003-2004 (2004)                                               Z Position (mm)
Strong Field Ionization of C+……

                                                                                 ISS for C2+ produced via C+ ionization
                                                                     1.6




                                        Integrated Ion Yield (arb)
                                                                     1.4
                                                                                                             C+ 2P - C2+ 1S
                                                                     1.2                                     C+ 4P - C2+ 1S
ISS results for ionization of C+ ions                                                                        C2+ 1S - C3+ 2S
                                                                     1.0
show ionization of groundstate and                                                                           Total Fit
                                                                     0.8                                     Experiment
higher lying metastable level.
                                                                     0.6

                                                                     0.4

                                                                     0.2

                                                                     0.0
                                                                           0.0        2.0       4.0    6.0         8.0         10.0

                                                                                            Focal Detuning (mm)




                                                       Can fit to ISS results by using saturated
                                                       volume method (El-Zein et al). Gives a
                                                       good indication of the ionization potential
                                                       for a particular process.
Strong Field Ionization of C+……

                                                                                 ISS for C2+ produced via C+ ionization
The IP from the saturated volume fits                                1.6

suggests;




                                        Integrated Ion Yield (arb)
                                                                     1.4
                                                                                                             C+ 2P - C2+ 1S
                                                                     1.2                                     C+ 4P - C2+ 1S
Groundstate:      C+ 2P  C2+ 1S                                                                             C2+ 1S - C3+ 2S
                                                                     1.0
                                                                                                             Total Fit
Metastable:       C+ 4P      C2+ 1S                                 0.8                                     Experiment

                                                                     0.6

                                                                     0.4

                                                                     0.2

                                                                     0.0
                                                                           0.0        2.0       4.0    6.0         8.0         10.0

                                                                                            Focal Detuning (mm)




                                        The metastable transition C+ 4P  C2+ 1S
                                        however is a forbidden transition.
                                        Requires an electron spin-flip event!

								
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