Patent ID: 8289524

Claim:
An interferometer, comprising: a light source, adapted to generate a coherent light beam; a body comprising a reference flat, adapted to both transmit a part of the coherent light beam as a measurement light beam and reflect another part of the coherent light beam as a reference beam; location means for locating an object to be measured having a measuring plane such that the measuring plane extends substantially parallel to the reference flat; a detector adapted to analyze a phase difference of the reference light beam and the measurement light beam; a first optical path from the light source to the object; a second optical path from the object to the detector, the first and the second optical paths have a common section in which the reference flat is located; and a first optical polarization modulator arranged in the first optical path and having a modulation frequency, wherein a distance between the reference flat and the object to be measured is equal to an integer multiple times Â¼ th a modulation period distance, the modulation period distance being light speed divided by the modulation frequency of the first optical polarization modulator.