Several methods of measuring multi-mode beam propagation characteristics are discussed. The aim is to use the minimum number of measurements and the simplest equipment possible. In theory all the beam properties can be determined from three beam diameter measurements. But care must be taken where the diameter measurements are made to avoid large errors due to small diffraction effects.
Steven C. Guggenheimer,
David L. Wright,
"Simple beam-propagation measurements on ion lasers", Proc. SPIE 1414, Laser Beam Diagnostics, (1 May 1991); doi: 10.1117/12.43660; https://doi.org/10.1117/12.43660