Implementation of 3D-focusing in an ion momentum spectrometer

An ion momentum spectrometer is used to acquire an ion’s three-dimensional (3D) momentum by measuring its time-of-flight and position. Recently, 3D-focusing techniques were implemented by several groups to improve energy resolution. Here, we build a 3D-focusing momentum spectrometer and apply the nonlinear parameter scaling rule to improve the ion kinetic energy resolution. In the experimental test, the O + /O + ion pairs are created by focusing 25 fs Ti: sapphire laser pulses on an O 2 molecular jet. In the kinetic energy release spectrum of O + /O + pairs, a resolution of 0.5 eV is obtained at 11.2 eV. Furthermore, the validity of the nonlinear parameter scaling rule is also confirmed in the analysis of O + /CO + ion pairs from CO 2 molecules. So it can be consistently applied to different ions in the spectrometer that uses a pure electric field.