The blue light in a ladder system: from double resonance optical pumping to Autler-Townes splitting

Abstract: In this experimental work we report our findings about a Ladder (Ξ) transition 5S_1∕2 → 5P_3∕2 → 5D_3∕2 of ⁸⁵Rb atoms under different laser power combinations. Based on the ratio of power levels of two individual lasers, which are used in counter-propagating configuration, the system exhibits double resonance optical pumping and Autler-Townes splitting. The excursion of the Ξ level coupling is studied alongwith photon counting of blue light originating from 5D_3∕2 → 6P_3∕2 → 5S_1∕2 non-degenerate decay. The blue photon statistics shows that emitted radiation are thermal. However the probability density of the integrated photon count vs. laser power exhibits a jump in intensity scale followed by a long tail, which resembles Lèvy type distribution. This may be considered as a signature when the level dressing changes in Ξ system as theoretically discussed earlier by Abi-Salloum [T.Y. Abi-Salloum, J. Mod. Opt. 57, 1366 (2010); T.Y. Abi-Salloum, Phys. Rev. A 81, 053836 (2010)]. Graphical abstract: [Figure not available: see fulltext.].