Scaling analysis parameters in 3D-focusing velocity map imaging

Abstract

Velocity map imaging spectrometer is a powerful tool for measuring the two-dimensional momenta of charged particles in dissociative photoionization processes. By combining a time-position sensitive detector with a three-dimensional (3D) source focusing mode, 3D momentum can be measured at a much higher resolution. However, due to the side effects of the non-uniform electric field in this mode, the retrieval of the 3D momentum becomes complicated. Here, we describe a method to retrieve the 3D momentum from the time of flight and the position at a numerical accuracy better than 0.1%, much below the best achievable relative energy resolution of 1% in the reported experiments. The method is consistently tested on simulated data, including ions with different masses and charges. Moreover, a scaling relationship is established among them.