ABSTRACT
The M2 model is currently the preferred way of quantitatively describing a laser beam, including its propagation through free space and lenses; specifically, as ratios of its parameters with respect to the simplest theoretical gaussian laser beam The present chapter describes the model and measuring techniques for reliably determining—in each of the two orthogonal propagation planes—the key spatial parameters of a laser beam; namely, the beam waist diameter 2W0, the Rayleigh range zR, the beam divergence Θ, and waist location z0.
