Intensity nonlinearity of the error-signal frequency shift in the modulation spectroscopy of dark resonances and approaches to its reduction

TL;DR

This paper investigates the intensity nonlinearity causing frequency shifts in dark resonance error signals during modulation spectroscopy, demonstrating its impact on atomic clock stability and proposing approaches to mitigate this effect.

Contribution

It reveals the intensity nonlinearity of error-signal frequency shifts in dark resonances and explores methods to reduce this effect for improved atomic clock performance.

Findings

Error-signal frequency can be displaced independently of intensity changes.

Displacement depends on system parameters as shown in experiments with $^{87}$Rb.

The effect potentially impacts clock stability and reproducibility.

Abstract

We have found that the error-signal frequency corresponding to the coherent population trapping resonance can be displaced from that of "$0-0$" transition unperturbed by the optical field, although the frequency is not sensitive to changes in its intensity. We consider the double $\Lambda$-system of levels interacting with the asymmetric polychromatic optical field to demonstrate that this effect arises due to intensity nonlinearity of the error-signal frequency shift. The experiment with $^{87}$Rb atoms in Ar-N$_2$ buffer gas atomic cell shows how the displacement value depends on different parameters. The possible influence of the effect on the clocks' frequency stability and reproducibility are discussed.