Modal decomposition by means of correlation filters has been proved as a key for real online laser beam analysis. To compare that method with the "standard" M2 method, we generated series of different laser beams (1064 nm), applied both methods to one and the same beam and evaluated achieved results. An adjustable Nd:YAG laser served as transversal mode generator, delivering diverse "pure" Gauss-Hermite modes and superpositions of modes, respectively. In the case of incoherent superposition of modes, their particular contribution to the general M2 value should be proportional to their relative strength, whereas in the case of coherent superposition M2 is distinctly influenced by phase differences between the discrete modal components. Achieved experimental findings are well confirmed by computer simulation.© (2009) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.