Abstract: This paper proposes a new interferometer to measure the roughness of optical disk substrates, which applies the principle of shearing interferometry and uses a Faraday modulator to detect the phase between two polarized beams. The instrument can produce surface probe and other statistical data with a height sensitivity of 2 nm and a lateral resolution of 1.2 $mu@m. It has excellent stability even under vibration conditions, and rapid and noncontact measurements can be made without a special reference surface. !11
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