Influence of chirping the Raman lasers in an atom gravimeter: phase shifts due to the Raman light shift and to the finite speed of light

TL;DR

This paper analyzes how frequency chirping of Raman lasers affects phase shifts in atom gravimeters, revealing biases in gravity measurements and emphasizing the importance of symmetric chirping to improve accuracy.

Contribution

It demonstrates that asymmetric chirping introduces measurement bias and shows that symmetric chirping reduces this bias, improving gravimeter precision.

Findings

Asymmetric chirping biases gravity measurements by microGal levels.

Symmetric chirping reduces phase shift biases in atom gravimeters.

The finite speed of light effect aligns with theoretical expectations.

Abstract

We present here an analysis of the influence of the frequency dependence of the Raman laser light shifts on the phase of a Raman-type atom gravimeter. Frequency chirps are applied to the Raman lasers in order to compensate gravity and ensure the resonance of the Raman pulses during the interferometer. We show that the change in the Raman light shift when this chirp is applied only to one of the two Raman lasers is enough to bias the gravity measurement by a fraction of $\mu$Gal ($1~\mu$Gal~=~$10^{-8}$~m/s$^2$). We also show that this effect is not compensated when averaging over the two directions of the Raman wavevector $k$. This thus constitutes a limit to the rejection efficiency of the $k$-reversal technique. Our analysis allows us to separate this effect from the effect of the finite speed of light, which we find in perfect agreement with expected values. This study highlights the benefit of chirping symmetrically the two Raman lasers.