Generalized Time-Reversal for Pulse Control in Diffusive Media

Abstract: Time-reversal symmetry allows waves to retrace their paths through complex media and refocus at their origin. However, incomplete capture and reversal of scattered waves often limits pulse recompression. We address this challenge for spatially extended sources by introducing a generalized time-reversal framework, which identifies the optimal source pattern as the one that maximizes the energy of the waves that are captured and reversed. In a two-dimensional diffusive waveguide, we reconstruct the time-reversed wavefront corresponding to this optimal source using spatiospectral shaping, leading to a 35-fold enhancement in peak transmitted power compared to an unmodulated pulse. Internal spatiotemporal measurements reveal a ``loading and firing" process, in which energy accumulates within the medium and then is released abruptly. Moreover, time-reversing this burst enables deep energy delivery into the scattering medium. Generalized time-reversal opens new possibilities for short-pulse control in strongly-scattering media, with applications ranging from optogenetics to random laser amplification.