A multi-axis interferometer uses a combined beam for a first pass through
the interferometer optics. Measurement and reference components of the
combined beam that exit the interferometer optics are subject to walk-off
that measurement or reference reflector misalignment can cause. A return
reflector and non-polarizing beam splitter system split the combined beam
into separated input beams for the various axes of the interferometer and
return the separated beams for respective second passes through the
interferometer optics. Walk-off for the separated beams in the
interferometer optics cancels the walk-off for the combined beam to
eliminate beam walk-off in separated output beams. Sharing a combined beam
for a first pass through the interferometer optics reduces the sizes
required for the interferometer optics and reference and measurement
mirrors. The multi-axis interferometer may have a single return reflector.
