Industrial high power fiber laser system with optical monitoring assembly

A high power fiber laser system for processing a workpiece is configured with a plurality of laser modules each having an output feeding fiber which supports and guides laser radiation towards the workpiece, and a fiber combiner formed upon coupling the output feeding fibers together and outputting the combined laser radiation into a delivery fiber. The combiner is configured so that the combined laser radiation has a minimally possible beam quality factor (M2). The high power laser system further includes a laser head receiving the combined laser radiation and focusing the latter on the surface of the workpiece so as cause a backreflected radiation to propagate backwards through the laser head, delivery fiber and combiner towards the laser modules. The fiber laser system also is provided with a monitoring assembly receiving the backreflected radiation and operative to detect the spectrum thereof.