Method and apparatus for measuring displacement of a sample

Abstract

In a displacement measurement apparatus using light interference, a probe light path is spatially separated from a reference light path. Therefore, when a temperature or refractive index distribution by a fluctuation of air or the like, or a mechanical vibration is generated, an optical path difference fluctuates between both of the optical paths, and a measurement error is generated. In the solution, an optical axis of probe light is brought close to that of reference light by a distance which is not influenced by any disturbance, a sample is irradiated with the probe light, a reference surface is irradiated with the reference light, reflected light beams are allowed to interfere with each other, and a displacement of the sample is obtained from the resultant interference light to thereby prevent the measurement error from being generated by the fluctuation of the optical path difference.

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