Heterodyne interferometer with subnanometer accuracy

This paper gives a brief description of the laser interferometer system designed for the next generation watt balance experiment aimed to realize the unit of mass by direct link to the Planck constant at the National Institute of Standards and Technology. The light source is an iodine-stabilized frequency-doubled Nd:YAG laser at λ=532nm. Three heterodyne interferometers with subnanometer non-linearity errors measure the angular and the vertical displacements of the induction coil.