High-Precision Method for Characterizing Degree of Collimation and Beam Quality for Application in Cold Atom Gravimeter System

Abstract

Highly collimated laser beam with excellent spatial quality is essential for quantum sensing experiments, where even small residual beam divergence can accumulate over distance and introduce significant systematic errors. In this article, we present the design and detailed characterization of a high precision laser beam collimator developed for a cold-atom Gravimeter system, capable of producing an expanded laser beam with a diameter of 16 mm while achieving microradian level collimation accuracy through a five-degree-of-freedom (5-DOF) adjustment mechanism. The beam quality is evaluated using an ISO11146 compliant beam propagation measurement combined with Gaussian beam analysis to extract key parameters, including the beam waist, divergence angle, Rayleigh length, and beam quality factor $M^{2}$. The measured divergence angles of 0.006° (105 micro-radian) along the $x$ axis and 0.007° (122 micro-radian) along the $y$ axis confirm stable and well controlled collimation over long propagation distances. The demonstrated collimation architecture and characterization methodology provide a robust and scalable solution for cold-atom Gravimetry and other precision optical applications that require stable, high quality laser beams maintained over extended distances.