In-beam tracking refractometry for coordinate interferometric measurement

Abstract

We propose to extend the principle of compensation of the fluctuations of the refractive index of air through monitoring the optical length within the measuring range of the displacement measuring interferometer. The concept is derived form a tracking refractometry evaluating the refractive index of air in the beam axis coinciding with the positioning interferometer. Application of this approach in multi-axis positioning and measurement mans to compromise the principle of spatial unity of the displacement measuring laser beam and the beam of the tracking refractometer. In this contribution we evaluate the level of uncertainty associated with the spatial shift of these two beams. Consequently the nature of the fluctuations of the refractive index of air in laser interferometry is investigated and discussed with the focus on potential applications in coordinate measuring systems and long-range metrological scanning probe microscopy systems.

Contribution of the Refractive Index Fluctuations to the Length Noise in Displacement Interferometry

“…Differential measurement with two, or four parallel beams would make things different, depending on the beam spacing. Correlation of the length noise observed by parallel beams was presented in [27] and shows that closely spaced beams in differential configuration could produce a compensative effect.…”