Polarization properties and temporal shapes of superradiance pulses in gases

The equations describing the polarization and temporal shapes of the superr adiance pulses formed in gaseous media on the transitions between degenerat e levels are obtained with an account of first-order atom-atom correlations . In these equations, unlike the semiclassical case, the initial conditions are well defined by the characteristics of the excitation pulse. The numer ical calculations of the superradiance pulse temporal shapes are carried ou t for some transitions with small values of the level angular momenta. Such calculations showed no qualitative difference with the results of semiclas sical approximation except the case of symmetric excitation, when the two p olarization components of superradiance are equal. In this latter case the superradiance pulse remains fully unpolarized, while in a semiclassical app roach it is considered to be fully polarized, its polarization varying rand omly from pulse to pulse. The results of the calculations indicate that in case of arbitrary values of the level angular momenta the coherent superrad iance pulse cannot depopulate the excited level totally, some part of the e xcited atoms (e.g., about 20 per cent in case of transitions 3/2 --> 3/2) i s depopulated in cause of incoherent spontaneous emission.