Abstract: Light that is initiated in a laser device includes a diffusion of scattered and reflected light around the laser beam. This diffusion of light occurs because light in the optical cavity of the laser is reflected from the surfaces of the bore and becomes misaligned, so that it leaves the laser along paths which are outside of the cone of light formed by the laser device. This diffusion of part of the laser light reduces the efficiency of the device and is objectionable in many applications. The diffused light is eliminated by providing a restriction in the optical cavity of the laser device which blocks off the stray or misaligned light. This restriction, or beam cleaner, may be positioned at various points along the axis of the optical cavity.