Interferometric apparatus and method for measuring motion along multiple axes

An interferometric method for measuring the translation of a body while being insensitive to pitch and yaw of the body as the body translates in mutually orthogonal directions, said interferometric method comprising the steps of:

• fixedly mounting a beam redirecting means to a body for translation therewith in at least two orthogonal directions;
• and
• forming a reference path for a reference beam;
• in combination with said beam redirecting means, forming a measurement path for a measurement beam having at least two pairs of incoming and outgoing segments where each incoming and outgoing segment in each pair travels, respectively, to and from said redirecting means along different paths that are vertically separated in a first direction while each pair of segments is laterally separated from one another in a direction orthogonal to that of said first direction, said measurement path changing in length as the body moves along a select one of said two orthogonal directions and being spatially separated from said reference path;
• introducing reference and measurement beams for travel along said reference and measurement paths, respectively;
• and
• combining said reference and said measurement beams so that they are coextensive and have a predetermined angle between them to generate an interference signal that varies in accordance with changes in said measurement path, said redirecting means being configured and arranged with respect to said optical means so that said reference and measurement beams remain substantially coextensive with said predetermined angle between them as the body moves both along said select direction and orthogonal to said select direction whereby said interference signal is insensitive to changes in the pitch and yaw of said body as it moves in said two orthogonal directions.

A distance measuring interferometer for measuring the translation of a body while being insensitive to changes in the pitch and yaw of the body as the body translates in mutually orthogonal directions, said distance measuring interferometer comprising:

• an X-Y translation stage;
• means for moving said X-Y translation stage along both X and Y directions;
• means for generating at least two spatially separated beams of radiation one of which is a measurement beam and the other of which is a reference beam;
• first beam redirecting means fixedly mounted with respect to said X-Y translation stage;
• second beam redirecting means mounted for movement with said X-Y translation stage;
• said first and second beam redirecting means being configured and arranged with respect to one another to intercept both said reference and measurement beams at least twice and redirect them through an angle of deviation of 180 degrees alone separate paths as reflected reference and measurement beam segments, respectively, that are spatially separated from one another such that the physical path over which said reference beam travels does not change with movement of said X-Y translation stage while the physical path over which said measurement beam travels changes in accordance with the X-translation of said X-Y translation stage and is independent of its Y-translation, pitch and yaw, said reflected reference and measurement beam segments remaining spatially separated as they emerge from said first and second reflection means, said measurement beam segments comprising at least two pairs of incoming and outgoing beam segments where each beam segment in a pair is spatially separated along a first direction and each pair of beam segments is spatially separated from the other along a direction that is orthogonal to said first direction;
• and
• means for combining said reflected reference and measurement beam segments so that they are coextensive to generate an interference signal that varies in accordance with changes in said measurement path, said first and second redirecting means being configured and arranged with respect to one another so that said reference and measurement beams remain substantially coextensive as said X-Y translation stage moves along both said X and Y directions whereby said interference signal is insensitive to changes of pitch and yaw of the body as it translates.