The Role of Doppler Broadening in Electromagnetically Induced   Transparency and Autler-Townes Splitting in Open Molecular Systems
  We describe in this Letter how inhomogeneous line broadening affects the Autler-Townes (AT) splitting in a three level open molecular cascade system. For moderate Rabi frequencies in the range of 300 to 500 MHz the fluorescence line shape from the uppermost level |3> in this system depends strongly on the frequency ratio of the two laser fields. However, the fluorescence spectrum of the intermediate level |2> appears as expected. We provide a description of the conditions for optimally resolved AT splitting in terms of the probe laser/coupling field frequency ratio and laser propagation geometry based on our theoretical analysis of the Doppler integral. This is important for applications such as molecular angular momentum alignment as well as for the measurement of the transition dipole moment matrix element. 
A. Lazoudis, E. Ahmed, L. Li, T. Kirova, P. Qi, A. Hansson, J. Magnes,   F.C. Spano and A.M. Lyyra