  The possibility to perform high-resolution time-resolved electron energy loss
spectroscopy has the potential to impact a broad range of research fields.
Resolving small energy losses with ultrashort electron pulses, however, is an
enormous challenge due to the low average brightness of a pulsed beam. In this
letter, we propose to use time-of-flight measurements combined with
longitudinal phase space manipulation using resonant microwave cavities. This
allows for both an accurate detection of energy losses with a high current
throughput, and efficient monochromation. First, a proof-of-principle
experiment is presented, showing that with the incorporation of a compression
cavity the flight time resolution can be improved significantly. Then, it is
shown through simulations that by adding a cavity-based monochromation
technique, a full-width-at-half-maximum energy resolution of 22 meV can be
achieved with 3.1 ps pulses at a beam energy of 30 keV with currently available
technology. By combining state-of-the-art energy resolutions with a pulsed
electron beam, the technique proposed here opens up the way to detecting
short-lived excitations within the regime of highly collective physics.
