Feedback spectroscopy of atomic resonances

TL;DR

This paper introduces a feedback-based spectroscopy method that enhances atomic resonance contrast and quality factor without needing a dense medium, confirmed through experiments with rubidium vapor.

Contribution

The paper presents a novel feedback control technique for spectroscopy that significantly improves resonance quality and contrast in optically thin media.

Findings

Resonance amplitude increased by one to two orders of magnitude.

Resonance width decreased threefold.

Contrast reached a record level of 260%.

Abstract

We propose a non-standard spectroscopic technique that uses a feedback control of the input probe field parameters to significantly increase the contrast and quality factor of the atomic resonances. In particular, to apply this technique for the dark resonances we sustain the fluorescence intensity at a fixed constant level while taking the spectra process. Our method, unlike the conventional spectroscopy, does not require an optically dense medium. Theoretical analysis has been experimentally confirmed in spectroscopy of atomic rubidium vapor in which a considerable increase (one-two order) of the resonance amplitude and a 3-fold decrease of the width have been observed in optically thin medium. As a result, the quality factor of the dark resonance is increased by two orders of magnitude and its contrast reaches a record level of 260%. Different schemes, including magneto-optical Hanle spectroscopy and Doppler-free spectroscopy have also showed a performance enhancement by using the proposed technique.