Event-mode Imaging Spectrometer



The advent of fast position sensitive particle detectors has made possible novel momentum space imaging techniques for studying the dynamics of ion, photon, and electron impact reactions with atoms or molecules. The basic concept behind this technique is simple: By measuring the momentum of all the charged particles produced in a single interaction, and applying the laws of conservation of momentum and energy, the interaction can be reconstructed a posteriori. These kinematically complete scattering experiments yield multi-dimensional pictures in momentum-space that often clearly reveal the underlying physical mechanism for the reaction.  Such an imaging system has recently been constructed in the CAMOS lab by the Jones group to study the dynamics of molecules exposed to intense laser fields.  After a laser-molecule interaction, electrons and molecular ions are guided by electric and magnetic fields to large area position sensitive delay line particle detectors.  The position and time of arrival of each charged fragment can be recorded on an event-by-event basis, allowing for reconstruction of the laser-molecule interaction.  Several experiments are underway on this apparatus, including studies of intense field ionization and dissociation of molecules and the development of time-dependent probes of molecular motion.