System including unified beamsplitter and parallel reflecting element, and retroreflecting component

A two-arm interferometer comprising, in combination:

• support means;
• combiner means comprising a unified beamsplitter element and a parallel reflecting element, for splitting entrant radiation into first and second beams moving in the same direction along parallel first and second paths;
• double-reflecting means, having opposite sides with substantially parallel plane reflective surfaces thereon, for reversely reflecting radiation impinging upon said surfaces in opposite directions along substantially parallel paths and without rotation of the impinging beams about their axes of propagation;
• retroreflecting means for retroreflecting radiation impinging thereupon along a third path that lies parallel to, and is displaced from, the path of the radiation impinging upon said retroreflecting means and with an orientation relative thereto rotated 180.degree. about its axis of propagation;
• and means for mounting said combiner means, said double-reflecting means, and said retroreflecting means on said support means, said retroreflecting means being disposed, for retroreflection, in said first path and with said second and third paths in substantial alignment with one another, and said double-reflecting means being disposed, for reflection from said opposite side reflective surfaces thereof, in both of said second and third paths, said means for mounting enabling translational movement of at least one of said retroreflecting means and said double-reflecting means, on axes parallel to said paths, and said interferometer being devoid of means, other than said retroreflecting means, operatively disposed in any of said paths and functional to effect any net rotational change about the axis of propagation of any beam.