An apparatus for spectral narrowing of high power diode laser arrays includes a high power diode laser array configured for production of an output light beam, a collimator configured for collimation of the output light beam, and a half-wave plate and polarizing beamsplitter positioned to receive the output light beam and to separate it into a feedback beam and a usable beam. The apparatus further includes an interference filter positioned to receive the feedback beam and form it into a filtered feedback beam. The filter has a narrow passband about a desired wavelength. The apparatus still further includes a cat's eye reflector to receive the feedback beam, direct it through the interference filter, and couple the filtered feedback beam into the diode laser array. A method for spectral narrowing of high-power diode laser arrays includes the steps of collimating the light output from the high power diode laser array; passing it through a beamsplitter to obtain feedback and usable beams; passing the feedback beam through an interference filter to form a filtered feedback beam; and coupling the filtered feedback beam back into the diode laser array.