After completing his doctorate, Poisson spent three years as a postdoctoral fellow in Kip Thorne's research group at the California Institute of Technology, in Pasadena. During this period, he became interested in the gravitational-wave signatures that black hole systems might produce. Such signatures are crucial for the operation of gravitational-wave detectors such as LIGO. This work continued for a subsequent year spent with Clifford Will at Washington University in St. Louis.