Beam quality M2 factor matrix for non-circular symmetric laser beams

Abstract

It is standard to use and to characterize the beam quality of a non-circular symmetrical beam on its x-axis and y-axis orientation. However, we knew that the values of and are inconsistent if one selects a different coordinate system or measures beam quality with different experimental conditionals, even when analyzing the same beam. To overcome this, a new beam quality characterization method, the M2 factor matrix, is developed. It not only contains the beam quality terms, and , to characterize the beam quality along x-axis and y-axis orientation for the non-symmetric beam, but also introduces two additional cross terms, Mxy and Myx, which are used to characterize the location relationship between the principal axis of the test beam and coordinate system in experiment. Moreover, M2 factor matrix can be measured with a similar procedure to the traditional M2 factor whose measurement instructions are described in ISO11146 by adding some additional image and signal processing procedure. The measurement principle and method is present and the experiment system for beam quality M2 factor matrix is built to demonstrate the performance of M2 factor matrix with real experiments.