27 January 1989 An Interferometer For Measuring Thickness And Spacing
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An interferometer utilizing a multielement photodetector has been developed to conduct fast and accurate measurement of the thickness of ultra-thin films and small spacing between two separated surfaces. The thickness of a magnetic film on a metallic substrate was measured. In addition, the spacing between a magnetic recording head and a glass disk surface was demonstrated. By examining the spectral intensity of the interference pattern, the film thickness or the spacing is calculated. The entire visible spectrum of the interference light beam is obtained simultaneously with the multielement photodetector. The spectral efficiencies of the light source and the diffraction grating as well as the spectrum response of the photodetector are measured for the calibration. Substrate effects are minimized by fist examining the reflection spectrum intensity of the substrate. A numerical filtering technique used in the experiments significantly reduces the noise, thereby yielding a good signal to noise ratio. An optical thickness of L/10 ( L is the wavelength ) is obtained by a carefully numerical analysis of the measured data, which is significantly less than the limitation, L/4, by the conventional method.
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Dong-sheng Wang, Dong-sheng Wang, Jin-wen Liang, Jin-wen Liang, "An Interferometer For Measuring Thickness And Spacing", Proc. SPIE 0965, Current Developments in Optical Engineering III, (27 January 1989); doi: 10.1117/12.948032; https://doi.org/10.1117/12.948032

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