High precision metrology systems based on heterodyne interferometry canmeasure position and attitude of objects to accuracies of picometer andnanorad, respectively. A frequently found feature of the general system designis the subtraction of a reference phase from the phase of the positioninterferometer, which suppresses low frequency common mode amplitude and phasefluctuations occurring in volatile optical path sections shared by both, theposition and reference interferometer. Spectral components of the noise atfrequencies around or higher than the heterodyne frequency, however, aregenerally transmitted into the measurement band and may limit the measurementaccuracy. Detailed analytical calculations complemented with Monte Carlosimulations show that high frequency noise components may also be entirelysuppressed, depending on the relative difference of measurement and referencephase, which may be exploited by corresponding design provisions. Whilst theseresults are applicable to any heterodyne interferometer with certain designcharacteristics, specific calculations and related discussions are given forthe example of the optical metrology system of the LISA Pathfinder mission tospace.
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