Tolerance analysis shows that an efficient <i>M</i><sup>2</sup> measurement plan is a first cut (beam diameter measurement) at 0.5–2.0 Rayleigh ranges to one side of the waist, which is matched by interpolation between second and third cuts to the opposite side. The waist is measured by a fourth cut halfway between the matched diameters, yielding an easy two-parameter curve fit for <i>M</i><sup>2</sup>.
© 1998 Optical Society of America
Thomas F. Johnston, "Beam Propagation (M2) Measurement Made as Easy as It Gets: The Four-Cuts Method," Appl. Opt. 37, 4840-4850 (1998)