Abstract

Dichromated gelatin (DCG) films are coated on substrates to make holographic optical elements (HOEs) by using various techniques. It is necessary to measure the thickness of these films before and after exposure and processing. It is also necessary to estimate the variation of the thickness at different areas of the substrate. This thickness range is usually between 5 03μm and 50 μm. The principle of the method is based on the measurements on the Haidinger fringes generated by the film. For ease of observation and measurement, a commercial Fizeau type interferometer such as ZYGO has been used. The simple modification to observe the Haidinger fringes with the Fizeau type interferometer will be described. The thickness of the film is related to the diameters of the Haidinger fringes. It is possible to estimate the thickness quickly by counting the number of fringes. A more accurate estimate can be obtained by the measurement of the diameters of the fringes and by using this data in a formula that will be described. It is possible to estimate the thickness of the film to within +1 μm. The method is entirely nondestructive.

© 1992 Optical Society of America