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Results using atomic targets

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.

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Results using atomic targets

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  1. 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.

  2. Groundstate Metastable ISS results for Ar+ ion beam…. • Using the Intensity Selective Scan (ISS) technique (see Experimental Setup presentation) Ar2+ production 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 increasing interaction volume with decreasing intensity as the lens moves away from zero. Ar2+ production from Ar+ ion beam (a) 1016 Wcm-2 (b) 5  1016 Wcm-2 • The groundstate peak at z = 0 therefore disappears rapidly compared to the metastable peaks at z = ±12 as the intensity decreases.

  3. 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 (a) neutral Ar and (b) Ar+ beam J. B. Greenwood et alPhys. Rev. Lett. 88. 233001 (2002) Note: (b) (i) Ar2+ and (ii) Ar3+ (x 50 vertical scale)

  4. ADK curves for Xe (circular intensity scaled x1.3) Xe+ g= 0.5 Xe2+ Unshifted 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. From ADK tunneling theory, Linear rate 1.3E0  Circular rate E0  For Circular field E0/ 2 (intensity I), matching Linear field is 1.3 x (E0/ 2) i.e. 0.81E0 (intensity 0.65I) Circular Intensity I Linear Intensity 0.65I

  5. Linear Circular Ne+ Ne2+ Experimental verification of intensity ratio of 0.65…. We experimentally verified the linear-circular intensity ratio of 0.65 by performing an ISS on Ne gas in the neutral gas target apparatus Ne was a good test gas to use as previous observations have found suppressed Nonsequential double ionization from this target (Becker and Faisel J. Phys. B 32 L335 (1999)) The results show excellent matching of the linear and circular yields for single and double ionization of Ne using the factor of 0.65. ISS for single and double ionization of Ne

  6. 131Xe2+ ISS results from Xe neutral target (linear polarization)…. Signal (arb.) Xe+ 129Xe2+ Time of Flight (sec) 132Xe2+ Xe8+ Temporally resolved isotopes of Xe2+ Z Position (arb.)

  7. Circular Linear Integrated Ion Yield (arb.) Z Position (mm) Linear-Circular ISS results for Xe and Xe+…. Xe  Xe+ Loss of linear flux in Xe+ appears as an enhanced linear signal in higher charge states Xe  Xe2+ Large enhancement of linear signal in the low intensity regions is due to the Nonsequential ionization! Xe  Xe3+ Suppressed Nonsequential component from the ionic target as was the case for Ar also! Xe+ Xe3+ For more information see : M. Sureshet al.RAL Annual Report 2003-2004 (2004)

  8. Strong Field Ionization of C+…… ISS results for ionization of C+ ions show ionization of groundstate and higher lying metastable level. 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.

  9. Strong Field Ionization of C+…… The IP from the saturated volume fits suggests; Groundstate: C+2P  C2+1S Metastable: C+4P  C2+1S The metastable transition C+4P  C2+1S however is a forbidden transition. Requires an electron spin-flip event!

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