: Du, K.-M.

Abstract
Many application results using high-power lasers show that to correlate the processing results with properties of the laser beam the average intensity distrubution and its propagation are necessary. Starting from statistical optics and using a set of suitable modes, the average intensity distribution and its propagation of laser beams are described by the mode coherence coefficients. Furthermore, temporal fluctuations of the laser power and intensity distributions impair all applications, notabyl those with high processing speed and high process quality. Depending on the interaction mechanism there is a characteristic time constant for a given process. The relevant instantaneous intensity defined by averaging the real instantaneous intensity over the characteristic time constant is introduced. The corresponding intensity fluctuation are describe using the variance and the spectrum of the local intensity.