Continuous temporal ion detection combined with time-gated imaging: Normalization over a large dynamic range

Imaging micro-channel plate (MCP) detectors are a common tool for chemical physics studies used to image a single ion mass species in a time-of-flight (TOF) spectrum. Temporal selection of the mass to be imaged is traditionally implemented by gating the voltage across the MCP stack, however this leads to the loss of all information about other species in the mass spectrum. Here we show that by gating the phosphor voltage instead, as has been demonstrated by Zajfman et al. (1995) among others, we gain the capability of measuring multiple masses in TOF while retaining the ability to image a single desired species. In our precision spectroscopy experiment, we image the spatial distribution of Hf⁺ photodissociation fragments, while its more plentiful HfF⁺ precursor, which arrives at a later time, can also be detected in TOF. This enables the shot by shot normalization of technical noise associated with the precursor production. Since the scheme alters only the configuration of the high-voltage switch, it can be readily implemented in most existing gated MCP setups, allowing the full TOF information to be harvested. Combining the imaging and TOF data in a single shot, we can detect species with substantially different abundances.