1. Results using molecular targets Linear-circular comparison of the intense field ionization of simple molecular targets (N 2, CO 2 ): evidence of nonsequential behaviour?? Temporal resolution of the different dissociation channels of CO 2 and N 2 molecular ions Comparison of the dissociation of laser-generated H 2 + (i.e. H 2 target) with that of H 2 + in the form of an ion beam generated using a discharge ion source

2. ISS Results for CO 2 The image shows a colormap of the Intensity Selective Scan (ISS) results from a CO 2 target. Clearly indicated are the various ionization and dissociation products separated temporally. The different Coulomb explosion channels produce forward (f) and backward (b) peaks through explosion towards or away from the detector.

3. Any evidence of Nonsequential Ionization?? Comparing the Linear-Circular polarizations should highlight any nonsequential processes occurring. One would expect this to appear as an enhancement in the double ionization of CO 2 with linear polarization. Given that there appears to be a loss of yield with linear polarization for both single and double ionization, this may as appear as a NS enhancement for higher charge states which subsequently dissociate into the fragment channels.

4. Fragment O 2+ dissociation channels… The TOFMS system can temporally resolve the various dissociation channels from CO 2 ionization. Shown to the left is a surface plot of the dissociation channels for O 2+ production as a function of intensity (focal detuning). The dissociation momentum is derived from the ions time-of-flight. (2,3,3)  O 2+ + C 3+ + O 3+ (2,2,3)  O 2+ + C 2+ + O 3+ (2,2,2)  O 2+ + C 2+ + O 2+ (1,2,2)  O + + C 2+ + O 2+

5. Nonsequential Ionization of N 2 … There is a clear enhancement of the double ionization of N 2 with linear polarization which is absent for the single ionization. This clearly indicates either nonsequential enhancement for the double ionization or molecular reorientation giving enhanced ionization along a preferential direction. Given that this reorientation effect seems to be absent for the N 2 + production its appears more plausible to the signature of nonsequential ionization.

6. Fragmentation channels for MEDI of N 2 … N 2+ N 3+ The different dissociation channels for N 2+ and N 3+ production are clearly visible. (2,1)  N 2+ + N + (2,2)  N 2+ + N 2+ (2,3)  N 2+ + N 3+ (3,2)  N 3+ + N 2+ (3,3)  N 3+ + N 3+ The highest charge state channels (2,3) and (3,3) appear closest to the centre of focus z = 0 mm (i.e. highest intensity). This is consistent with them requiring the highest ionization stage of the N 2 q+ ion. When they Coulomb explode they impart the greatest K.E. in the fragment ions and thus the forward/backward peaks show the largest time separation.

7. Fragmentation channels for MEDI of N 2 … Given in the table are the kinetic energy release (KER) values per fragment ion determined from the timing information for each of the dissociation channels for N +, N 2+ and N 3+ production (~ 2x10 16 Wcm -2, 55fs ). The calculated values are based on Coulomb explosion at the equilibrium internuclear separation. The experiemental KER values are almost half of that expected for dissociation at the equilbrium internuclear separation. This suggests the N 2 q+ ions in fact dissociate at almost twice this bond length. This is consistent with previous observations and is explained by theoretical models* as dissociation at a critical internuclear separation whereby the ionization probabitility is maximum at this enlarged bond length. *J. H. Posthumus et al., J. Phys. B, 28, L349 (1995) *T. Seideman et al., Phys. Rev. Lett., 75, 2819 (1996)

8. Strong Field Ionization of H 2 … The ISS intensity range covers all three ionization regions, multiphoton ionization (MPI), tunnelling (T) and over- the-barrier field ionization (FI). These regions are characterised by the Keldysh parameter, . Multiphoton Ionization:  > 1 Tunnelling Ionization: 0.5 <  < 1 Over-the-barrier:  < 0.5 The graph shows the deconvoluted ISS results for H 2 ionization. The deconvolution technique removes the volume effect of ISS from the results.

9. Comparison of H 2 + dissociation: laser + discharge generated… H + from laser generated H 2 + H from discharge generated H 2 +

10. Comparison of H 2 + dissociation: laser + discharge generated… H + from laser generated H 2 + H from discharge generated H 2 + The high energy dissociation peak centred around 0.4-0.5 eV is from Coulomb explosion of the ionized H 2 +. Two other weaker photodissociation peaks are also apparent, the 1 photon (~0eV) and the 2 photon. The signal falls to zero around 7mm from the focus indicating H + production only at the high intensity region ( > 5x10 13 Wcm -2 ). The Coulomb explosion detected for H + isn’t detected as we are only detecting the neutrals. There is therefore a large loss of flux at highest intensity where Coulomb explosion will occur. The peak at zero energy extending to around 0.4eV would appear to be a combination of 1  and 2  dissociation. The signal is detected over a much larger intensity range than for the laser-generated case as the initial ionization stage of H 2 which requires highest intensity is removed.