ABSTRACT
The phenomenon of interference is known since the period of Newton. It accounts for the colours observed on oil sleeks and soap bubbles. Shear interferometry became very popular as shear could be realized with a plane parallel plate. This was also the period when computers became available to optical physicists and electronics was utilized more and more for the analysis of the interferogram. In shear interferometers, the interference is observed between a wave front and its sheared version; there is no need to have a reference wave front. The interferometer is illuminated by the light from a moving target; that is, it is illuminated by a Doppler-shifted light. If the velocity of the target is changing, then the wavelength of light reflected from the target is also changing with time. The cyclic interferometer is used in laser ring gyroscopes based on Sagnac effect.
