an optical beam mode controlled high power laser system having a resonator which incorporates therein as one of the reflective elements a high efficiency diffraction grating . impinging upon the diffraction grating is not only the high power resonator laser beam , but also an injected mode controlling laser beam of preselected wavelength . each beam is directed at the diffraction grating at a predetermined angle in order for the grating to direct away therefrom a combined beam of radiant energy having high power and being locked to the preselected wavelength of the injected laser beam . it is this high power laser beam of preselected wavelength which is output from the laser system .