A quasi-translator for economically producing pure, smooth translational motion with broad arcuate or error-free motion regardless of orientation, which is useful in numerous interferometer applications including spectroscopy, a Fourier modulator and a Fourier spectrometer are provided. The quasi-translator utilizes a support, an arm including a driving magnet on a first end and a driven element on a second end, an axis for rotation of the arm, a bearing system that controls the rotation of the arm about the axis, a drive coil and a drive amplifier to drive the arm in the arcuate motion. The quasi-translator may be employed in a Fourier modulator to change the optical path difference of the interferometer/quasi-translator at a substantially constant rate of change. The quasi-translator and/or Fourier modulator may be used in a Fourier spectrometer to create an optical spectrum from a light beam and/or electrical signal created from the light beam.