Interferometer optical system

An interferometer optical system for measuring the optical parallelism of first and second spaced subject mirrors comprising,

• a source of spacially coherent radiation directed along an initial path,
• a target for said radiation,
• means for splitting said radiation along said initial path into two beams, a first beam and a second beam,
• first optical means for directing the first beam normal to said first subject mirror,
• second optical means for directing said second beam normal to the second subject mirror,
• the first optical means includes first, second and third mutually perpendicular mirrors which intercept the first beam from the beam splitting means and combines with said beam splitting means and said first spaced mirror to define a first optical path,
• the second optical means includes a fourth mirror which intercepts the second beam from the beam splitting means and combines with said beam splitting means and the second subject mirror to define a second optical path,
• the first, second, third and fourth mirrors and the beam splitting means, without the two spaced mirrors in the system, define a closed optical path for both the first and the second beams over which these beams each return to a point of origin at the beam splitting means, whereat the returned first and second beams are superimposed one upon the other and directed along a common output path to the target and
• said two subject mirrors are located along said closed path between the third and fourth mirrors,
• whereby when said two spaced mirrors are so placed in the system, the superimposed first and second beams along the common output path directed to the target reveal an interference pattern which is indicative of the degree of non-parallelism of the two spaced mirrors.