Abstract Specifically adapted diagnostic methods are required both for industrial use and for the scientific further development of thermal coating processes. The two optical diagnostic methods, particle flux imaging (PFI) and particle shape imaging (PSI), are assigned to one of these two tasks. The PFI process enables the monitoring and quality control of the entire spraying process right through to the formation of layers. PSI diagnostics is basically a shadow image process in which a cw laser is used to illuminate the particles in the spray jet. The Linspray PFI-method is assigned to the group of diagnostics which are used for monitoring the total process. Particle characteristics as size, shape and velocity are derived for PSI by an automatic image processing. It would be furthermore interesting to measure on-line the size of the particles in the jet and to study the correlation of the particle size and other particle characteristics. Paper includes a German-language abstract.