We demonstrate an improved imaging system that can achieve highly efficient 3D detection of two electrons in coincidence. The imaging system is based on a fast frame complementary metal-oxide semiconductor camera and a high-speed waveform digitizer. We have shown previously that this detection system is capable of 3D detection of ions and electrons with good temporal and spatial resolution. Here, we show that with a new timing analysis algorithm, this system can achieve an unprecedented dead-time (<0.7 ns) and dead-space (<1 mm) when detecting two electrons. A true zero dead-time detection is also demonstrated.
With a novel three-dimensional electron-electron coincidence imaging technique and two-electron angular streaking method, we show that the emission time delay between two electrons can be measured from tens of attoseconds to more than 1 fs. Surprisingly, in benzene, the double ionization rate decays as the time delay between the first and second electron emission increases during the first 500 as. This is further supported by the decay of the Coulomb repulsion in the direction perpendicular to the laser polarization. This result reveals that laser-induced electron correlation plays a major role in strong field double ionization of benzene driven by a nearly circularly polarized field.
We report a combined experimental and theoretical study to elucidate nonsequential double ionization dynamics of argon atoms at laser intensities near and below the recollision induced ionization threshold. Three-dimensional momentum measurements of two electrons arising from strong field nonsequential double ionization are achieved with a novel electron-electron-ion coincidence apparatus, showing laser intensity dependent Coulomb repulsion effect between the two outgoing electrons. Furthermore, a previously predicted feature of double ionization from doubly excited states is confirmed in the distributions of sum of two-electron momenta. A classical ensemble simulation suggests that Coulomb-repulsion-assisted double ionization from doubly excited states is at play at low laser intensity. This mechanism can explain the dependence of Coulomb repulsion effect on the laser intensity, as well as the transition from side-by-side to back-to-back dominant emission along the laser polarization direction.
we report the first state-resolved electron momentum correlation measurement of strong field nonsequential double ionization in benzene. With a novel coincidence detection apparatus, highly efficient triple coincidence (electronelectron-dication) and quadruple coincidence (electron-electron-cation-cation) are used to resolve the final ionic states and to characterize three-dimensional (3D) electron momentum correlation. The primary states associated with dissociative and non-dissociative dications are assigned. For the first time, a 3D momentum anticorrelation is observed for the electrons in coincidence with dissociative benzene dication states while such a correlation is absent for non-dissociative dication states.
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