An Optical Metrology System for Delay Position Measurement in a Dispersed Fourier Transform Spectrometer

A dispersed Fourier transform spectrometer (dFTS) was used to measure the radial velocity of stellar targets. A mechanical-based metrology system intrinsically built into the dFTS instrument was enhanced with a laser-based optical metrology system. Precisions of the optical path difference within the instrument were brought from about 20 nm to 0.1 nm resulting in highly precise radial velocity measurements on the order of 1.5 m/s. Without the optical metrology system radial velocity measurements were only precise to about 300 m/s. The stability of the dFTS instrument was measured by calculating the zero-point radial velocity over the operational time of the instrument using a thorium-argon line-spectrum light source.