Day: November 2, 2026

In short Five common definitions, one beam. D4σ (second moment), 1/e² clip, FWHM, knife-edge 10/90 and 86.5% power content give the same diameter only for a clean Gaussian beam. D4σ is the reference. It is the ISO 11146 width, it is defined for any beam shape and it is the width used for M². It […]

Why bench far-field measurements understate laser beam divergence, how the focal-plane method gives it exactly (Θ = d_f / f), a worked 1064 nm example, common mistakes and a beam divergence calculator.