Abstract
In this article we have shown that the atomic states can be engineered by tunning the coupling Rabi frequency for a system with $\mathcal{N}$-type configuration. Electromagnetically induced transparency (EIT), Electromagnetically induced absorption (EIA) and Autler-Townes (AT) splitting has been observed experimentally in a four level $\mathcal{N}$-type atomic vapor of $^{85}Rb$ atoms in the hyperfine levels of $D_2$ transition. It has been shown that the response of the atomic medium can be tunned from highly transparent to highly absorptive in our case. The evolution of the atomic states from the dark state |D> to the non-coupled state |NC> has been studied with the partial dressed state approach which makes the backbone of the modification of the atomic response. In addition, transient solutions in the time domain and steady state solution in the frequency domain has been studied. The population dynamics and the coherence contribution in each case has been analyzed by the time dependent solutions. The experimentally observed steady line-shape profiles has been supported by the steady state solution of optical-Bloch equations considering the Maxwell Boltzmann velocity distributions of the atoms. It has been observed that the crossover between the EIT and the AT splitting has been replaced by the interference contribution of the EIA in this $\mathcal{N}$-type system.
Highlights
Atomic coherence is a kind of knob to control the medium response coherently
Like the Electromagnetically induced transparency (EIT), another coherent phenomena is electromagnetically induced absorption (EIA) [10,11,12] which can be observed with three beam spectroscopy
The coupling beam was taken from ECDL1 and the probe beam was generated by downshifting the coupling beam by 120 MHz with the help of an acousto optic modulator (AOM)
Summary
Induced transparency (EIT) [1] is such a gate that can be created in a three level atom interacting with two beams. Three beam spectroscopy can be more interesting than the former because it is preferable in order to study the non-linear properties of the atomic medium [9]. Like the EIT, another coherent phenomena is electromagnetically induced absorption (EIA) [10,11,12] which can be observed with three beam spectroscopy. Due to EIA, the system becomes highly absorptive and sharp spectral features can be observed, which have several applications in precision spectroscopy. Lezama et al [10] had shown that a minimum four level atomic system is necessary to achieve the EIA. Subluminal to superluminal light can be observed in this system [15]
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