Light-intensity susceptibility and "active" noise spectroscopy

TL;DR

This paper introduces the concept of light-intensity susceptibility (LIS) for active optical noise spectroscopy, demonstrating its ability to reveal detailed quantum system properties through spectral analysis of modulated optical responses.

Contribution

It proposes a linear approximation method using LIS to analyze the response of multilevel quantum systems to noise-modulated optical fields, expanding the capabilities of noise spectroscopy.

Findings

LIS spectrum can reveal ground-state structure and optical transition properties.

The approach is effective with fast spectrum analyzers.

Calculations on a four-level system demonstrate the method's potential.

Abstract

In this paper, we consider informative potentialities of the "active" optical noise spectroscopy, under which we understand, generally, spectroscopy of response of a multilevel quantum system to the resonant optical field with its intensity modulated by "white" noise. We show that calculations of such a response can be most conveniently performed, in the linear approximation, by introducing the notion of light-intensity susceptibility (LIS) whose spectrum is determined by Laplace transform of the response to a small step-wise change of the optical field intensity. The results of calculations for a simple four-level quantum system show that its LIS spectrum may provide information not only about the ground-state structure (like conventional Faraday-rotation-based spin noise spectroscopy), but also about properties of the optical transitions (including nutation frequencies in the applied optical field). From the experimental point of view, such a noise spectroscopy of the intensity-related susceptibility can be especially efficient in combination with the up-to-date spectrum analyzers providing extremely fast data processing.