Multiparticle Cumulant Mapping for Coulomb Explosion Imaging

Abstract

We extend covariance velocity map ion imaging to four particles, establishing cumulant mapping and allowing for measurements that provide insights usually associated with coincidence detection, but at much higher count rates. Without correction, a four-fold covariance analysis is contaminated by the pairwise correlations of uncorrelated events, but we have addressed this with the calculation of a full cumulant, which subtracts pairwise correlations. We demonstrate the approach on the fourbody breakup of formaldehyde following strong field multiple ionization in few-cycle laser pulses. We compare Coulomb explosion imaging for two different pulse durations (30 fs and 6 fs), highlighting the dynamics that can take place on ultrafast timescales. These results have important implications for Coulomb explosion imaging as a tool for studying ultrafast structural changes in molecules, a capability that is especially desirable for high-count rate x-ray free electron laser experiments.

Two-Dimensional Projected-Momentum Covariance Mapping for Coulomb Explosion Imaging

“…Several ion imaging studies have also made use of 3-fold covariance analysis .25ex2ex c o v ( A , B , C ) = ⟨ ( A − false⟨ A false⟩ ) ( B − false⟨ B false⟩ ) ( C − false⟨ C false⟩ ) ⟩ infix= ⟨ A B C ⟩ − ⟨ A B ⟩ ⟨ C ⟩ − ⟨ A C ⟩ ⟨ B ⟩ − ⟨ B C ⟩ ⟨ A ⟩ + 2 ⟨ A ⟩ ⟨ B ⟩ ⟨ C ⟩ either to assign a three-body fragmentation pathway , or elucidate new information about the parent ion structure . Recently, procedures to extend the analysis further to four-or-more-particle correlations have also been derived and demonstrated experimentally …”

“…Several ion imaging studies have also made use of 3-fold covariance analysis either to assign a three-body fragmentation pathway , or elucidate new information about the parent ion structure . Recently, procedures to extend the analysis further to four-or-more-particle correlations have also been derived and demonstrated experimentally …”

“… 51 Recently, procedures to extend the analysis further to four-or-more-particle correlations have also been derived 52 and demonstrated experimentally. 53 …”

“…51 Recently, procedures to extend the analysis further to four-ormore-particle correlations have also been derived 52 and demonstrated experimentally. 53 Contingent Covariance. Due to the nature of covariance analysis, it relies on stable experimental conditions.…”

The Role of Momentum Partitioning in Covariance Ion Imaging Analysis

“…Collectively, these results shed light on the fragmentation behavior of 1/2-IP polycations and demonstrate the usefulness of covariance imaging analysis to study nuclear dynamics induced by inner-shell ionization. Given the recent developments in extending statistical correlation techniques to higher order correlations (involving four or more particles ,, ) and the progress in high-repetition-rate FELs, ,, we anticipate that this approach will yield a highly sensitive probe of the many-body fragmentation dynamics of highly charged polycations. Such a probe is the basis for Coulomb explosion imaging, generated by either deep single-photon inner-shell ionization of heavy elements or multiphoton ionization in intense fields. ,,,− …”