We present a simple mathematical model giving a possible description of a partially coherent light beam exhibiting a flat-topped transverse intensity profile. Such a model allows us to deduce the modal distribution inside a multimode stable optical cavity, assuming that the modes are of the Hermite–Gauss type. The analytical expression used to represent flat-topped profiles is of the flattened Gaussian type and leads to an exact, closed-form expression for the M2 factor of the output beam. An analogous procedure could be used to treat the general problem of deducing the modal distribution inside a laser cavity starting from intensity measurements of the output beam.
© 1998 Optical Society of America
Riccardo Borghi and Massimo Santarsiero, "Modal decomposition of partially coherent flat-topped beams produced by multimode lasers," Opt. Lett. 23, 313-315 (1998)