A method for measuring the degree of contamination of a protective glass of a laser processing head and laser processing system for implementing the method

A method for measuring the degree of contamination of a protective glass (9) which is supported by a laser machining head (1) and radiating the output side existing in a in the laser machining head (1) lens assembly (7), passes through the laser beam (5), in which - by continued an outside of the laser beam (5) arranged first radiation detector assembly (13) by the laser beam (5) surface of the protective glass (9) is observed to measure the intensity of there coming scattered radiation (12) generated by scattering of the laser beam (5) of particles (11) is caused to adhere on the protective glass (9) - a second radiation detector assembly (16) measures the intensity of a laser beam from the (5) deflected partial beam, and further wherein - a of the first radiation detector assembly (13) measured scattered radiation measured value to that of the second radiation detector assembly (16) is compared with a reference scattered radiation measured value is set measured radiation measurement value in relationship to obtain a corrected scatter radiation measurement, to a first upon exceeding of the latter to produce error signal, wherein the second radiation detector assembly (16) of the first radiation detector assembly (13) facing radially.