title: 2pi ambiguity-free optical distance measurement with subnanometer precision with a novel phase-crossing low-coherence interferometer.
abstract: We report a highly accurate phase-based technique for measuring arbitrarily long optical distance with subnanometer precision. The method employs a Michelson interferometer with a pair of harmonically related light sources, one cw and the other low coherence. By slightly detuning (~2 nm) the center wavelength of the low-coherence source between scans of the target sample, we can use the phase relationship between the heterodyne signals of the cw and the low-coherence light to measure the separation between reflecting interfaces with subnanometer precision. As this technique is completely free of 2pi ambiguity, an issue that plagues most phase-based techniques, it can be used to measure arbitrarily long optical distances without loss of precision. We demonstrate one application of this technique, the high-precision determination of the differential refractive index.
authors.forename: Changhuei
authors.initials: C
authors.lastname: Yang
authors.forename: Adam
authors.initials: A
authors.lastname: Wax
authors.forename: Ramachandra R
authors.initials: RR
authors.lastname: Dasari
authors.forename: Michael S
authors.initials: MS
authors.lastname: Feld