A self-injection locking system was disclosed in United States Patent #4,982,406 dated Jan. 1, 1991. The device internally narrows a prepulse of a laser cavity before it is replicated as the laser output. This system contains two quarter wave plates, an air spaced etalon, and a polarizing beam splitter. The air spaced etalon separates the off-center frequency signals from the center frequency signals. This is done by inducing a phase shift. Following this, the polarizing beam splitter impedes the off-center frequency signals by a power loss of about ten percent. The center frequency signals are unaffected. In operation, this can cause the off- center frequency signals to fail to reach the threshold at which stimulated emission takes place. The result is that the laser replicates only the center frequency signals as the laser output.