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Journal of Modern Optics

Atomic coherence induced Kerr nonlinearity enhancement in Rb vapour

Hai Wang, David J. Goorskey, Min Xiao

Published Mar 1, 2002• 34 citations
Publisher

Abstract

The Kerr nonlinear index of refraction for rubidium atoms is measured by using an optical ring cavity with and without electromagnetically induced transparency (EIT). Significant enhancement and inhibition of the Kerr nonlinear index is observed near resonance with EIT. The nonlinear index of refraction is measured as functions of probe and coupling frequency detunings, respectively, with and without the presence of EIT. A simple theoretical calculation including Doppler broadening is presented and is found to be in good qualitative agreement with the experimentally measured results.

DOI
10.1080/09500340110089938

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The Kerr nonlinear index of refraction for rubidium atoms is measured by using an optical ring cavity with and without electromagnetically induced transparency (EIT). Significant enhancement and inhibition of the Kerr nonlinear index is observed near resonance with EIT. The nonlinear index of refraction is measured as functions of probe and coupling frequency detunings, respectively, with and without the presence of EIT. A simple theoretical calculation including Doppler broadening is presented and is found to be in good qualitative agreement with the experimentally measured results.
Summary form only given. We present our recent results in measuring the nonlinear Kerr index of refraction of multi-level rubidium atoms inside an optical ring cavity. By using a similar experimental arrangement as we used previously to demonstrate cavity linewidth narrowing due to EIT inside an optical ring cavity, we can measure the nonlinear coefficient χ/sup (3)/ through the asymmetric transmission profile of the ring cavity. By measuring the degree of asymmetry, we can obtain the Kerr nonlinear index of refraction directly, without worrying about contributions from linear absorption. Our preliminary results indicate a significant enhancement of Kerr nonlinearity due to atomic coherence at near-resonance conditions. We present our experimental results and their comparison with theoretical calculations. We discuss the implications of this enhanced nonlinear Kerr index of refraction to nonlinear optical processes in an optical cavity.
Summary form only given. The reduced absorption and enhanced nonlinearity in a three-level electromagnetically induced transparency (EIT) system are very important in achieving an effective all-optical switching action. The Kerr-nonlinear index of refraction of a three-level EIT medium can be greatly enhanced near resonance due to atomic coherence induced in such a system in comparison with a two-level atomic system, as we have shown by using an optical ring cavity. Both the magnitude and sign of the Kerr-nonlinear index change dramatically for different frequency detunings of the controlling (or coupling) or cavity (or probe) field. Bistability and dynamic instability occur when such a three-level /spl Lambda/-type EIT system is placed inside an optical ring cavity and the controlling and cavity input intensities to exceed certain threshold values. In this paper, we present a recent experimental demonstration of controlling the cavity output intensity by modulating the frequency detuning of the controlling beam.
The potential to precisely control both the linear and nonlinear index of refraction through optical manipulation of the atomic states has recently pushed warm alkali vapors to the forefront of research in the field of quantum sensors, quantum memories, and quantum fluids of light. Rubidium (Rb) vapor in centimeter-scale glass cells or millimeter-scale micro-electro-mechanical system (MEMS) cells has proven to be a very promising platform for these applications, yet only a handful of research works have been dedicated to the investigation of the (non)linear refractive index of Rb vapor. We present results of theoretical calculations of the (non)linear refractive index of warm Rb vapor, based on the optical Bloch equations for 6-level Rb atoms interacting with a probe laser. They are compared to the experimental results obtained using an interferometric technique, showing very good quantitative agreement. A Kerr nonlinear refractive index n2 of up to −1.2×10−4 cm2/W is obtained. Python scripts for all theoretical calculations presented in this work are provided, including the refractive index calculation, that can readily be used in practical implementations for simulating the (non)linear refractive index of Rb vapor including the effects of Doppler broadening, transit time broadening, pressure broadening, saturation, optical pumping, and spin-exchange collisions.
The potential to precisely control both the linear and nonlinear index of refraction through optical manipulation of the atomic states has recently pushed warm alkali vapors to the forefront of research in the field of quantum sensors, quantum memories, and quantum fluids of light. Rubidium (Rb) vapor in centimeter-scale glass cells or millimeter-scale MEMS cells has proven to be a very promising platform for these applications, yet only a handful of research works have been dedicated to the investigation of the (non)linear refractive index of Rb vapor. We present results of theoretical calculations of the (non)linear refractive index of warm Rb vapor, based on the optical Bloch equations for 6-level Rb atoms interacting with a probe laser. They are compared to the experimental results obtained using an interferometric technique, showing excellent quantitative agreement. A Kerr nonlinear refractive index n2n_2n2​ of up to 10−410^{-4}10−4 cm2^22/W is obtained. Python scripts for all theoretical calculations presented in this work are provided, including the refractive index calculation, that can readily be used in practical implementations for simulating the (non)linear refractive index of Rb vapor including the effects of Doppler broadening, transit time broadening, pressure broadening, saturation, optical pumping, and spin-exchange collisions.
We show that long-lived bright Zeeman coherence that is responsible for absorption enhancement and steep anomalous dispersion in an atomic medium gives rise to a giant nonlinearity of the atomic susceptibility, in a similar manner to the dark coherence responsible for the well-known electromagnetically induced transparency. The intensity dependent refractive index of Cs vapour with a ground state Zeeman coherence in the vicinity of the D2 resonance line has been measured at low light intensity. The Kerr nonlinearity in the bright coherent state (n2 approx 1.0 × 10-6 cm2 mW-1) is higher than that in a dark state under the same experimental conditions. Higher order nonlinear components of the refractive index have also been estimated for both coherent states.