Experimental study of photon-echo size in optically thick media

We have studied the effect of generative-pulse amplitude, spatial profile, and temporal character as well as medium optical thickness on the power of photon and stimulated echoes. Working in atomic Yb vapor, photon echoes are observed that, absent material relaxation, are more powerful than the firs t generative pulse, thereby exceeding typically expected photon-echo powers by approximately two orders of magnitude. Factors crucial to the generatio n of powerful echoes identified through Maxwell-Bloch simulation are experi mentally confirmed. [S1050-2947(99)51308-5].