Alignment system with double-beam coincidence

To decrease laser tube drift, earlier improvements in laser tube construction and other parts were rather complicated.1 The alignment system presented is simple. When an original laser beam passes through the double-beam coincidence system, it will first split into two beams which are reversed with respect to each other; then the two coincide into one. The drift of the original beam can be compensated in the coincided beam. Some experiments were performed using a vacuum pipe.