A wavelength scanning interferometer for measuring the surface\udand thickness of a transparent film has been studied. A halogen light source\udcombined with an acousto-optic tuneable filter is used to generate a\udsequence of filtered light in a Linnik interferometer, which leads to a\udsequence of interferograms captured by a CCD camera. When a transparent\udthin film is measured, the reflection signals from both the top and bottom\udsurfaces of the film will interfere with the reference signal. At the same\udtime, the multiple reflection signals between the two film surfaces will also\udinterfere with each other. Effective separation of the interference signals\udfrom each other is the key to achieving a successful measurement. By\udperforming a frequency-domain analysis, these interference signals can be\udseparated. An optimized Fourier transform method is used in the analysis.\udMeasurements of the top and bottom surface finishes of the film, as well as\udthe film thickness map, have been achieved. The film needs to be more than\ud3 μm in optical path length, and must transparent with no absorption of\udlight. The film’s refractive index needs to be known as a function of\udwavelength. In this paper, the theoretical analysis and simulation study of\udwavelength scanning interferometry for transparent film measurement is\uddiscussed. Experiments on thin film layers of Parylene N coated on a glass\udslide surface are studied and analyzed. Comparison study results with other\udcontact and non-contact methods are also presented
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