interference pattern that clearly shows the deformation. Because wave front differences of a fraction of a wavelength of light thus become visible, this method is extremely sensitive for deformation studies. Another important application is the storage of digital data, which can be recorded as bright and dark spots in holographic images. A hologram can contain a large number of pages that are recorded at different angles relative to the plate, thus allowing the storage of a very large amount of data on one hologram. By illuminating the hologram with a laser beam at different angles, the pages can be read out one by one.InterferometerInstrument that utilizes the phenomenon of interference of light waves for the precise measurement of wavelengths of light itself, of small distances, and of certain optical phenomena. Because the instrument measures distances in terms of light waves, it permits the definition of the standard meter in terms of the wavelength of light.Many forms of the instrument are used, but in each case two or more beams of light travel separate optical paths, determined by a system of mirrors and plates, and are finally united to form interference fringes. In one form of interferometer for measuring the wavelength of monochromatic light, the apparatus is so arranged that a mirror in the path of one of the beams of light can be moved forward through a small distance, which can be accurately measured, thus varying the optical path of the beam. Moving the mirror through a distance equal to one-half of the wavelength of the light causes one complete cycle of changes in the pattern of interference fringes. The wavelength is calculated by measuring the number of cycles caused by moving the mirror through a measured distance.Uses When the wavelength of the light used is known, small distances in the optical path can be measured by analyzing the interference patterns produced. This technique is used to measure the surface contou...
