Wave front-splitting phase shift beam splitter for pencil beam interferometer

A beam splitter to create two separated parallel beams is a critical part of the pencil beam interferometer. Beam splitters can be separated into two categories based upon their operating principle: amplitude splitting or wave front splitting. A wave front-splitting phase shift beam splitter (WS-PSBS) with a monolithic structure and equal optical path is described that is well suited to the stability requirements of a pencil beam interferometer. Several techniques to produce a WS-PSBS are presented. In addition, the WS-PSBS using double thin plates or a single plate, made from microscope cover plates, has great advantages of economy, convenience, availability, and ease of adjustment over other types of beam splitters. A comparison of stability measurements made with the WS-PSBS and other equal optical path beam splitters is presented. The pencil beam interferometer using the WS-PSBS can achieve a stability of 0.45 μrad root mean square over 15–24 h periods.