Characterization of a two-color pump-probe setup FLASH using a velocity map imaging spectrometer

We report on the implementation of a high-count-rate charged particle imaging detector for two-color pump–probe experiments at the free electron laser in Hamburg (FLASH). In doing so, we have developed a procedure for finding the spatial and temporal overlap between the extreme UV free electron laser (FEL) pulses and the IR pulses, which allows for complete alignment of the setup in situations where the region of overlap between the FEL and the IR is not easily accessible by means of imaging optics.