Optical EngineeringReal-time measurement of one-dimensional step profile with a sinusoidal wavelength-scanning interferometer using double feedback control
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A linear CCD image sensor is used to electrically scan a measuring point and measure 1-D step-profiles in real time with a sinusoidal wavelength-scanning (SWS) interferometer using double feedback control. In this interferometer, the optical path difference (OPD) and the amplitude of the SWS are controlled so that a ruler marking every wavelength and a ruler with scales smaller than a wavelength are generated. These two rulers enable us to measure an OPD longer than a wavelength in real time. Two different step profiles with step heights of 1 and 20 μm, respectively, are measured with a measurement error of less than 8 nm. Measuring time for one measuring point is 0.04 s.