Inhomogeneous broadening-dependent spectral features in a four-level atomic system

New spectral features in an inhomogeneously broadened N-type four-level ato mic system are analyzed and discussed. The atomic-level scheme uses an inco herent pumping rate in place of the incoherent recycling pump. We show that the gain profile includes an extra dip that appears only in the Doppler-br oadened case. The dependence of this feature on various parameters, as well as consequences for the dispersion, are explored theoretically. For certai n combinations of temperature and incoherent pump rate, this gain is shown to be independent of temperature fluctuations. (C) 2000 Optical Society of America [S0740-3224(00)01602-7].