Determining the tilt of the Raman laser beam using an optical method for atom gravimeters

Abstract

Abstract The tilt of Raman laser is a major systematic error in precision gravity measurement using atom interferometry. The conventional approach to evaluate this tilt error involves modulating the direction of the Raman laser and conducting time-consuming gravity measurements to identify the error minimum. In this work, we demonstrate a method to expediently determine the tilt of the Raman laser by transforming tilt angle measurement into parallelism characterization, which integrates the optical method of aligning the laser direction, commonly used in freely-falling corner-cube gravimeters, into atom gravimeters. A position sensing detector (PSD) is utilized to quantitatively characterize the parallelism between the test beam and the reference beam, thus measuring the tilt precisely and rapidly. After carefully positioning the PSD and calibrating the relationship between the distance measured by the PSD and the tilt angle measured by tiltmeter, we achieved a statistical uncertainty of less than 30 μrad in the tilt measurement. Furthermore, we compared the results obtained through this optical method with those from the conventional gravity measurement tilt modulation method. The comparison validates that our optical method can achieve tilt determination with an accuracy level of better than 200 μrad，corresponding to a systematic error of 20 μGal in g measurement. This work has practical implications for real world applications of atom gravimeters.