Raman and non Raman EIT resonances in a degenerate four level system

TL;DR

This paper explores novel non Raman dark states in a degenerate four-level atomic system, revealing their polarization-dependent properties and demonstrating their occurrence in hydrogen atoms under different temperature conditions.

Contribution

It introduces and analyzes non Raman dark states that do not require two-photon resonance, expanding understanding of coherence effects in multi-level atomic systems.

Findings

Non Raman dark states do not need two-photon resonance.

Polarization geometry determines non Raman resonance conditions.

Non Raman resonances occur in hydrogen atoms at various temperatures.

Abstract

We study coherence effects in an atom having three metastable levels and single life-time broadened upper state. Two laser fields couple ground states to an excited one and an radio-frequency (rf) field operates between ground state levels. We consider the case when the common level for the rf-field and one of the laser field (to which we refer as the probing field) transitions is twice degenerate. We predict a novel type of dark states (we call them non Raman dark states), which in contrary to Raman resonances, do not require the fulfillment of the two-photon resonance condition. We realize the configuration in the atomic hydrogen and show that non Raman resonances are determined by the geometry of the rf and probing field's polarizations. For ultra-cold atoms non Raman resonances arise when the polarization vectors of the fields are parallel or perpendicular to each other. For an atomic gas at room temperatures electromagnetically induced transparency (EIT) resonances associated with Raman and non Raman dark states are studied by taking into account spin-exchange relaxation in the ground state of the hydrogen atom. We establish properties of non Raman dark states by investigating the relation of EIT resonances to the polarization geometry.