Optical amplification by dynamical gratings

Summary form only given. We describe in particular a density grating obtained from the interaction between a strong e.m. pump field and an atomic vapor, which allows for the amplification of a probe field. Experimental results and an interpretation are offered in this case, together with suggestions for possible applications resulting from these systems. In particular we present a recent experiment that shows the combined effects of the two fundamental aspects of quantum optics, in the spontaneous generation, through momentum transfer between light and atoms, of a long range atomic density grating. The experiment is performed in a vapor of atomic sodium at temperatures between 460 and 800K