Saturation Aided Non-Linear Absorption in a Double Λ System of EIT

Md. Mabud Hossain, S. Mitra, Biswajit Ray +1 more

Hamid Reza Hamedi, Ali Khaledi‐Nasab, Ali Raheli

Andal Narayanan, Preethi Thekkile Madathil, Manukumara Manjappa

We experimentally observe a non-linear absorption resonance in one of the two probe beams of a double Λ system which is interacting with three optical beams. This probe beam counterpropagates to the other two beams, both of which are co-propagating. The absorption resonance in this probe beam arises due to interaction between the dark states of the double Λ created by the co-propagating beams. The double Λ configuration of levels is in the D2 hyperfine manifold of 87Rb atoms, and the interaction is studied at room temperature. The non-linear absorption resonance is shown to be a three-photon process arising whenever the two co-propagating beams satisfy the two-photon Raman condition, necessary for electromagnetically induced transparency. Through a dressed state analysis, we show that the absorption feature is a result of interference between the absorption pathways to the excited states, from the ground states of the double Λ. The non-linear nature of the probe beam absorption enables it to perform like a directional optical switch. This absorption switch operates conditioned on non-absorption of a single photon of the same frequency due to a coherent process, in a beam traveling in the opposite direction.

Martin Gärttner, Jörg Evers

Md. Mabud Hossain, S. Mitra, P Poddar +3 more

Atomic coherence resonances such as electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA) signals are observed in a Doppler broadened multi-level system for the D 2 line of 85 Rb atoms in a vapour cell considering different types of atom–laser coupling schemes. Besides the coherence resonances, the nonlinear resonances like velocity selective optical pumping (VSOP) dips and velocity selective resonances (VSR) are also observed for the non-zero velocity selective groups of atoms. In the presence of pump, control and probe laser fields, we observe two EIT signals in a double Λ-type system and two EIA signals in a double V -type system. We are able to see the EIA signal for the non-zero velocity group of atoms when the pump laser is locked with an open transition by a small red detuning. We also report the experimental observation of simultaneous EIT and EIA signals in a (Λ+ V )-type system. The effect of frequency tuning of the control laser is also studied in the presence of the frequency locked pump laser. A simple theoretical analysis explains the experimental results.

Min Xiao, Baolong Lü, W. H. Burkett

The atomic coherence effect can be used in enhancing the efficiencies of nonlinear optical processes. Particularly, nondegenerate four-wave mixing (NDFWM) in multilevel systems has recently gained attention in connection with the advantage of using coherent population trapping (CPT) or electromagnetically induced transparency (EIT) to enhance the efficiency of generated signals. Generally speaking, linear absorption competes with the nonlinear signal generation at the exact one-photon resonance condition. However, the linear absorption can, in principle, be reduced or even eliminated by preparing the system in the CPT or EIT state. We report experimental demonstrations of NDFWM in several multi-level configurations in rubidium atomic vapor. In one of the double-/spl Lambda/ systems an unusual behavior of signal output power as a function of pump power, i.e. a maximum in the generated signal power is reached as the pump power increases, is experimentally observed. By comparing with several related /spl Lambda/ and double-/spl Lambda/ systems, we have concluded that CPT is the mechanism for this interesting effect.