Time-resolved ion imaging at free-electron lasers using TimepixCam.

The application of a novel fast optical-imaging camera, TimepixCam, to molecular photoionization experiments using the velocity-map imaging technique at a free-electron laser is described. TimepixCam is a 256 × 256 pixel CMOS camera that is able to detect and time-stamp ion hits with 20 ns timing resolution, thus making it possible to record ion momentum images for all fragment ions simultaneously and avoiding the need to gate the detector on a single fragment. This allows the recording of significantly more data within a given amount of beam time and is particularly useful for pump-probe experiments, where drifts, for example, in the timing and pulse energy of the free-electron laser, severely limit the comparability of pump-probe scans for different fragments taken consecutively. In principle, this also allows ion-ion covariance or coincidence techniques to be applied to determine angular correlations between fragments.

Photon counting phosphorescence lifetime imaging with TimepixCam.

TimepixCam is a novel fast optical imager based on an optimized silicon pixel sensor with a thin entrance window and read out by a Timepix Application Specific Integrated Circuit. The 256 × 256 pixel sensor has a time resolution of 15 ns at a sustained frame rate of 10 Hz. We used this sensor in combination with an image intensifier for wide-field time-correlated single photon counting imaging. We have characterised the photon detection capabilities of this detector system and employed it on a wide-field epifluorescence microscope to map phosphorescence decays of various iridium complexes with lifetimes of about 1 µs in 200 µm diameter polystyrene beads.