Weak space charge effects in laser multiphoton ionization of a rarefied gas beam of heavy species

Abstract

We experimentally explore weak space charge effects (SCEs) in multiphoton ionization (MPI) experiments using C60 as an example of heavy species. The laser-induced delayed ionization of C60 was used to prepare a photoion pulse with a decreasing initial charge density distribution from a start value that is one order of magnitude smaller than the density limit (3☓108 ions/cm3) proposed previously to assume that the SCEs can be negligible. The photoion spectra at different time slices of the photoion pulse were measured using a velocity map imaging spectrometry. This allows us to quantify the SCEs on the photoion spectra in such low-density and heavy-species regime. The weak SCEs explored here can help us to understand and improve the temporal-spatial resolutions in those high-precision measurements.