Method for direct measurement of the variance of laser beams.

A method permitting direct measurement of the spatial variance along a given transverse direction of any laser beam is described. The procedure relies on the use of a transmission filter whose local transmissivity varies spatially as an inverted parabola. The variance and the first moment of a transverse beam intensity distribution are readily obtained simply by measurement of the maximum power transmitted through the filter as this filter is moved across the beam's section.