Laser beam characterization by means of modal decomposition versus M2 method

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 globall 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 findings are well conrmed by computer simulation.