Abstract
A high resolution heterodyne laser interferometer without periodic nonlinearity for linear displacement measurements is described. It uses two spatially separated beams with an offset frequency and an interferometer configuration which has no mixed states to prevent polarization mixing. In this research, a simple interferometer configuration for both retroreflector and plane mirror targets which are both applicable to industrial applications was developed. Experimental results show there is no detectable periodic nonlinearity for both of the retro-reflector interferometer and plane mirror interferometer to the noise level of 20 pm. Additionally, the optical configuration has the benefit of doubling the measurement resolution when compared to its respective traditional counterparts. Because of non-symmetry in the plane mirror interferometer, a differential plane mirror interferometer to reduce the thermal error is also discussed.
Highlights
Since the Doppler frequency shift measurement technology using a two-frequency source was invented in the 1970s, heterodyne laser interferometry has been widely used as an accurate positioning sensor to measure displacements of precision stages [1]
A simple interferometer configuration for both retroreflector and plane mirror targets which are both applicable to industrial applications was developed
The optical configuration has the benefit of doubling the measurement resolution when compared to its respective traditional counterparts
Summary
Since the Doppler frequency shift measurement technology using a two-frequency source was invented in the 1970s, heterodyne laser interferometry has been widely used as an accurate positioning sensor to measure displacements of precision stages [1]. When the geometrical errors are minimized, periodic nonlinearity is the fundamental error source limiting the implementation of subnanometer displacement measurements. This assumes the measurement is performed in an ideal environment, such as in vacuum, or when the measurement length minimized so the refractive index effects are minimal. We describe two simple heterodyne interferometer configurations, with a retroreflector and with a plane mirror, with two spatially separated beams to eliminate the periodic nonlinearity. These interferometers have a minimum number of optical components and the opposite phase shift direction between interference signals enhances the optical resolution by a factor of two. This optical resolution enhancement allows for simpler optical configurations while achieving the same optical resolution by increasing the number of beam paths in the interferometer
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