Time focus with velocity imaging of charged particles in coincidence: Application to photoionization of CO and N₂O

A coincidence spectrometer combining time-focusing optics with velocity imaging has been developed to achieve high velocity resolution for both positive and negative particles. Positional broadening of particle images and temporal broadening of particle flight times caused by an extended source volume are effectively cancelled by the design of the electrostatic lenses. The performance of the new optics is demonstrated in photoionization of CO. Sample results are presented on dissociative photoionization from CO⁺(D²π) and N₂O⁺(C²Σ⁺), where molecular frame photoelectron angular distributions are obtained for the first time with vibrational resolution of both initial state and diatomic products.