Quantitative evaluation and removal of periodic error caused by ghost reflections in a double-path homodyne interferometer

Abstract

Abstract This paper discusses periodic error caused by ghost reflections in a double-path homodyne interferometer, which is difficult to be removed by so-called Heydemann’s method due to its unique frequency. The mechanism of the periodic error is represented by a theoretical equation established focusing on the number of round trips of a measurement light path. Based on the theory, it was found that specific periodic errors are caused by the measurement light reflected on one surface of an optical element. To evaluate the presence and removal of the periodic error, the self-evaluation method, which was extended to include ghost reflections, was applied. Experimental evidence shows that a wedge provided on that surface prevents unwanted reflections and reduces the periodic error to approximately 2 pm.