Compensation of wavelength dependent image shifts in imaging optical interferometry.

In modern interferometers for absolute length measurements, when applying phase stepping interferometry, several different wavelengths are used as light sources, and the interferogram is projected to a CCD-camera array. Such interferometers are equipped with wedged optical components as windows and beam splitters, to prevent additional interferences. The wedged optics causes the position of a test piece within the interferogram related to the camera pixel coordinates to be dependent on the wavelength used. This effect depends on the wedge angles and the thicknesses of optical components as well as on their distances within the interferometer's optical pathway. We give a quantitative analysis and suggest a compensation of this dispersion effect by an additional wedge plate outside the interferometer.