On-site calibration of the Raman laser absolute frequency for atom gravimeters

Abstract

The length standard for atom gravimeters is defined by Raman laser wavelength, which, in turn, depends on the absolute laser frequency. Here we present a method to measure Raman laser frequency based on an atom gravimeter itself, which has an advantage of calibrating the length standard on-site. The calibration utilizes the ${D}_{2}$ line of $^{87}\mathrm{Rb}$ atoms as a reference and takes advantage of the cold atom free fall as well as developed techniques of evaluating hyperfine-level shift within atom gravimeters. A calibration accuracy of 1 part in ${10}^{10}$ is achieved for the Raman laser frequency, which constrains the corresponding error below 1 $\ensuremath{\mu}\mathrm{Gal}$ in our gravity measurement.