Temporal and spatial behavior of photon echoes stimulated from long pulses

To evaluate the coherent saturation effects of continuous optical processing using optical coherent transients we studied the time dependence of the photon echoes stimulated by probe fields with constant amplitudes and durations comparable to the coherent dephasing time. The propagation directions of the long echoes were also found to be different from brief pulse echoes. Echoes in the non-causal direction were predicted with a theory based on Maxwell–Bloch equations, observed experimentally, and explained analytically.