  We present a new approach for spatiotemporal focusing through complex
scattering media by wave front shaping. Using a nonlinear feedback signal to
shape the incident pulsed wave front, we show that the limit of a
spatiotemporal matched filter can be achieved, i.e., the wave amplitude at the
intended time and focus position is maximized for a given input energy. It is
exactly what is also achieved with time-reversal. Demonstrated with ultrasound
experiments, our method is generally applicable to all types of waves.
