Abstract
Displacement measuring interferometers, commonly employed for traceable measurements at the nanoscale, suffer from non-linearities in the measured displacement that limit the achievable measurement uncertainty for microscopic displacements. Two closely related novel non-linearity correction methodologies are presented here that allow for the correction of non-linearities in cases where the displacement covers much less than a full optical fringe. Both corrections have been shown, under ideal conditions, to be capable of reducing all residual non-linearity harmonics to below the 10 pm level.
Highlights
Optical interferometry provides a direct route for traceability to the SI metre on length scales for which direct time of flight measurement is impractical [1]
A small non-linearity component with an amplitude of 8 pm can be seen at a spatial period of 105.5 nm for all algorithms, corresponding to λ/6, which in this interferometer system appears to be introduced by internal reflections within the solid glass corner cube retroreflector
As demonstrated in figure 5, the multiple intensity reference (MIR) algorithm is highly sensitive to any effect that results in incomplete interference between the beams returned from each arm, with twice per fringe nonlinearities rising to 50 pm in the presence of wavefront distortions from a solid glass corner cube seam
Summary
Optical interferometry provides a direct route for traceability to the SI metre on length scales for which direct time of flight measurement is impractical [1]. For measurements made at the nanoscale, optical interferometry provides the primary route to traceability. Whilst a number of other technologies, including capacitive sensors [2], grating based encoders [3] and x-ray interferometry [4] are able to make high accuracy displacement measurements at the nanoscale, all rely upon optical interferometry for traceability [1].
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