Coherent pulsations in the vibrational fluorescence of CO and NO in solid N₂

Infrared laser pumping of the v = 2 level of CO and NO molecules dispersed in liquid-helium-cooled N₂ crystals results in vibrational stimulated emission (VSE) on the v = 2 → v = 1 transition. VSE is characterized by strong undamped pulsations whose intensity exceeds in some cases that of the regular spontaneous fluorescence by a factor of 100. Numerical computations have been carried out using a model describing the interaction of the field building up at the 2→1 band center with the inhomogenously broadened medium. The occurence of spontaneous coherent pulsations very similar to that experimentally observed is strongly related to the long dephasing time and to the strong spectral inhomogeneity of the vibrational lines of CO and NO in solid N₂.