Fig. 1

a Schematic of the spontaneous RBS, where the light is scattered by the spontaneous density fluctuations in the gas. b Schematic of the coherent RBS, where the light is Bragg-diffracted on the gas density fluctuations created by two pump beams. By phase matching, the signal beam follows, in reverse, the path of pump beam 1. Reprinted figure with permission from [50]. Copyright (2002) by the American Physical Society