Distinction between double electromagnetically induced transparency and double Autler-Townes splitting in RF-driven four-level ladder 87Rb atomic vapor

In this paper, the physical origin of interferences has been explored in a four-level cascade rubidium atom by simultaneous interaction with three energies; two optical fields and one radio frequency (RF) field. The atomic system is investigated by a combination of the analytical method introduced by Zhu et al (2010 Phys. Rev. A 81 053836) and resonant pole method introduced by Anisimov (2008 J. Mod. Opt. 55). A substantial amount of variation in the probe absorption has been observed in various regimes. The transition from electromagnetically induced transparency (EIT) to Autler-Townes spitting (ATS) is observed. It is found that a definite threshold value exists governing the crossover from EIT to ATS. The applied analytical method gives a clear insight into the nature of interferences; one may observe EIT as a consequence of destructive interference, whereas ATS is a consequence of constructive interference. Furthermore, a transition from single EIT to double electromagnetically induced transparency has been detected when the system is illuminated by RF-driving field in weak control regime. Further, transition from ATS to double Autler-Townes splitting has been observed in the strong control regime.