Design and fabrication of a variable frequency grating and its application as a lateral-shear interferometer having a variable shear

The design and fabrication of holographic gratings of frequency variable from 50 to 750 lines/mm over length of 75 mm have been described. An application of these variable frequency gratings as a lateral-shear interferometer has also been suggested. The variable shear interferometer is found to be useful for testing of lenses with a maximum sensitivity in the detection of wavefront aberrations. Comparison of single-frequency grating having uniform pitch of 100 lines/mm with a grating of frequency variable from 59 to 220 lines/mm using an average pitch of 100 lines/mm over a small area as a lateral-shear interferometer have been made. Our experimental observations show that a small area of average pitch of 100 lines/mm on the grating having a variable frequency of 59-220 lines/mm over a distance of 75 mm behaves as a lateral-shear interferometer in the same way as any area of pitch of 100 lines/mm on the grating of uniform pitch of 100 lines/mm