Using digital holographic microscopy to study transparent thin films

This paper presents the first experimental results of using a digital holographic interference microscope (DHIM) to study thin transparent films (with thickness less than the wavelength of visible light) on transparent substrates. The DHIM makes it possible not only to obtain a three-dimensional image of the film surface, but also to carry out quantitative measurements. Coatings composed of aluminum nitride (AlN) on acrylic substrates are used as the films, which can be used to protect items made from acryl from the action of the surroundings. Surface defects existing on the surface of the coatings and resulting from the action of UV radiation on the coating and the substrate have been studied. The method of classical optical microscopy for investigating thin transparent films has been compared with the possibilities of the method of digital holographic microscopy. The results confirmed that it is efficient to use DHIM for such studies. (C) 2009 Optical Society of America.