Optical frequency shifting of a mode-locked laser beam

An optical frequency shifter making use of the electro-optic effect in LiNbO
3
was built to shift the Fourier spectrum of a mode-locked He-Ne laser; the shift was continuously adjustable from -45 GHz to +45 GHz about the central optical frequency of 473.61 THz. Shifted Fourier spectra recorded with a scanning Fabry-Perot interferometer were found to be in excellent agreement with theory.