3D Velocity Map Imaging of Electrons

Traditionally velocity map imaging (VMI) experiments only measure the momenta of particles transverse to the time of flight axis and recover the the momentum in the direction of time of flight axis by Abel inversion or other means. Although in previous work we measured the 3D momentum of photoions using a fast camera, electrons have a much lower spread in their time of arrival. Hence, so far it has not been possible to resolve 3D momenta of electrons.

We present a technique to measure 3D VMI of electrons using an event based camera (TPX3CAM), which has a built-in fast time to digital converter (TDC) with a time resolution of 260ps. As usual the transverse momentum is obtained by the camera's sensor and we trigger the camera's TDC by the electrical signal from the phosphor screen. This allows us to implement 3D VMI for electrons without modifying the underlying VMI or the vacuum system.

This new technique, along with voltage switching, will allow us to measure 3D momenta of ions and electrons in coincidence. This very simple implementation of momentum resolved coincidence measurements can play an important role in time resolved spectroscopy.