Multiple-beam lateral-shear interferometer

A Ronchi ruling is photographed through a phase object that deforms the grating lines. The object is displaced longitudinally, and a second exposure is made. After developing, the photographic plate is observed with a frequency-plane mask that cuts off all but one of the diffracted orders. A lateral-shear interferogram of the phase object is obtained in this way. The experiment may be carried out by making multiple exposures and by displacing the object through equal distances after each exposure. This will produce a multiple-beam lateral-shear interferogram, and the fringes become very sharp.