Effects of thermal motion on electromagnetically induced absorption

Abstract

We describe the effect of thermal motion and buffer-gas collisions on a four-level closed N system interacting with strong pump(s) and a weak probe. This is the simplest system that experiences electromagnetically induced absorption (EIA) due to transfer of coherence via spontaneous emission from the excited to ground state. We investigate the influence of Doppler broadening, velocitychanging collisions (VCC), and phase-changing collisions (PCC) with a buffer gas on the EIA spectrum of optically active atoms. In addition to exact expressions, we present an approximate solution for the probe absorption spectrum, which provides physical insight into the behavior of the EIA peak due to VCC, PCC, and wave-vector difference between the pump and probe beams. VCC are shown to produce a wide pedestal at the base of the EIA peak, which is scarcely affected by the pump-probe angular deviation, whereas the sharp central EIA peak becomes weaker and broader due to the residual Doppler-Dicke effect. Using diffusion-like equations for the atomic coherences and populations, we construct a spatial-frequency filter for a spatially structured probe beam and show that Ramsey narrowing of the EIA peak is obtained for beams of finite width.

Electromagnetically induced absorption in a nondegenerate three-level ladder system

“…More recently, EIA has been observed in a degenerate lambda system [17] and also in a four-level N -system [18], even when the degeneracy is lifted by applying a small magnetic field. The effects of thermal motion have also been investigated [19].Here we present the first experimental observation of EIA in a non-degenerate three-level ladder system. In a thermal 87 Rb vapour, the degeneracy is lifted by a strong magnetic field, in which the atoms enter the hyperfine Paschen-Back regime [20][21][22] where all transitions are separated in frequency by more than the Doppler width.…”

“…More recently, EIA has been observed in a degenerate lambda system [17] and also in a four-level N -system [18], even when the degeneracy is lifted by applying a small magnetic field. The effects of thermal motion have also been investigated [19].…”

Recovering the Homogeneous Absorption of Inhomogeneous Media

“…Therefore, full recovery of the homogeneous absorption cross-section requires both a narrow transition for the recovery field γ r γ and a high intensity of the coupling and recovery fields µ 2 1. It is important to distinguish between the mechanism we study and those developed for enhancing the homogeneous absorption in degenerate multilevel systems [34][35][36][37][38]. These mechanisms circumvent the multilevel structure of the transition and thus can only increase the absorption up to that originating from the strongest transition in the manifold [36].…”

Tunneling induced absorption with competing Nonlinearities

“…EIT originates from destructive interference between different optical paths that causes the system to exhibit transparency for an incident pulse within a narrow spectral range with steep dispersion3. In contrast, EIA is a result of constructive interference due to transfer of coherence in Zeeman-degenerate systems4. Most recent research is concerned with multi-photon coherence processes56789 and is carried out in multilevel atomic systems, including Lambda-, cascade- and N-type systems101112.…”