  Time reversal mirrors have been successfully implemented for various kinds of
waves propagating in complex media. In particular, acoustic waves in chaotic
cavities exhibit a refocalization that is extremely robust against external
perturbations or the partial use of the available information. We develop a
semiclassical approach in order to quantitatively describe the refocusing
signal resulting from an initially localized wave-packet. The time-dependent
reconstructed signal grows linearly with the temporal window of injection, in
agreement with the acoustic experiments, and reaches the same spatial extension
of the original wave-packet. We explain the crucial role played by the chaotic
dynamics for the reconstruction of the signal and its stability against
external perturbations.
