Compact beam re-tracing optics to eliminate beam walk-off in an interferometer

An interferometer comprising:

• optics that split an input beam into a reference beam and a measurement beam and directs the measurement beam for at least one reflection from a measurement reflector on an object being measured, the optics recombining the reference and measurement beams into a combined beam in which the reference and measurement beams are parallel but subject to walk-off that depends on the alignment of the measurement reflector;
• a beam splitter system;
• and
• a return reflector positioned to receive the combined beam and direct the combined beam into the beam splitter system, wherein:
• the beam splitter system splits the combined beam into a plurality of separated beams and directs the separated beams into optics;
• and
• the optics split each of the separated beams into a separated reference beam and a separated measurement beam and directs each of the separated measurement beams for a least one reflection from the measurement reflector, for each of the separated beams, the optics recombining the separated reference beam and the separated measurement beam to form a merged beam in which the separated reference and measurement beams are collinear.

A method for operating an inteferometer comprising:

• directing an input beam into interferometer optics that split the input beam into a reference beam and a measurement beam, cause the measurement beam to reflect from a reflector mounted on an object being measured, and recombine the measurement and reference beams to form a combined beam that is output from the interferometer optics;
• splitting the combined beam into a plurality of separated beams;
• directing the separated beams into the interferometer optics, wherein for each separated beam, the interferometer optics split the separated beam into a reference beam and a measurement beam, cause the measurement beam to reflect from the reflector mounted on the object being measured, and recombine the reference and measurement beams to form an output beam corresponding to the separated beam;
• and
• analyzing the output beams to determine measurements along multiple axes.

A multi-axis interferometer comprising:

• a polarizing beam splitter positioned to split an input beam into a combined measurement beam and a combined reference beam;
• a measurement reflector system including a plane mirror positioned to receive the combined measurement beam from the polarizing beam splitter;
• a reference reflector system including a plane mirror positioned to receive the combined reference beam from the polarizing beam splitter;
• a first retroreflector positioned to receive the combined measurement beam and the combined reference beam after respective first reflections from the measurement reflector system and the reference reflector systems, the first retroreflector sending the combined measurement beam and the combined reference beam back into the polarizing beam splitter;
• a return reflector that reflects an incident beam in a manner such that shifting the incident beam results in a matching shift of a reflected beam, the return reflector being positioned to receive the combined measurement beam and the combined reference beam;
• and
• a non-polarizing beam splitter system that splits the combined measurement beam into a plurality of separated measurement beams that are directed into the polarizing beam splitter and splits the combined reference beam into a plurality of separated reference beams that are directed into the polarizing beam splitter.