Our Series SP-D double plane-mirror interferometers are designed for incorporation into customer-supplied systems, and are used for simultaneously making pairs of nanoprecision length measurements. The differences in these pairs of length measurements and the separations between their two beams are then used for accurately determining the associated angles involved, where the maximum tolerated angular misalignment is approximately two minutes of arc and varies with beam separation. In cases involving small length changes, focusing their external beams on the objects being measured allows increasing the maximum toleratedangular misalignment to ± 30 minutes of arc.

Their laser light sources are coupled to their sensor heads via fiberoptic cables. Their miniature interfero-meters convert motions of their moving mirrors into pairs of optical-interference signals that are transmitted to their electro-nic power-supply/signal-processing modules for processing. Their He-Ne lasers, which are frequency stabilized on models designed for making longer length measurements, along with corrections for environmental shifts in laser wavelength, provide the basis for their high metric precisions. A PC running custom software package is employed for operating their electronics modules and displaying measurement results.