Abstract: A method and system for automatically aligning a high power laser utilizing diffraction ruled reflection grating to sample the laser beam. A tiltable beam alignment mirror directs a laser beam in a path incident to the reflection grating which separates the incident beam into a reflected beam and first and second order diffraction beams. A tiltable distortion compensation mirror is positioned in the path of the two diffraction beams. Two auxiliary fixed mirrors are positioned such that the diffraction beams will reflect a predetermined number of times off the distortion compensation mirror prior to reflecting toward respective null position detectors. Error signals from these detectors are translated, in accordance with certain optical and mathematical relationships, into angular adjustments to the two tiltable mirrors, thereby compensating for the thermal distortion of the reflection grating and aligning the output laser beam.