| 摘要 |
An apparatus is provided for measuring a spacing between an object to be measured T and a transparent object 4. The transparent object 4 is disposed, facing a surface of the object to be measured T, light is emitted to impinge through the transparent object 4 onto the object to be measured T, and the spacing is calculated based on an intensity of interference light occurring in a facing portion between the surface of the object to be measured T and the transparent object 4. The apparatus comprises a light source 1 for emitting light, a modulator 2 for modulating an intensity of the emitted light with modulation waves having a predetermined frequency, a sensor 7 for converting the light intensity of the interference light into an electrical signal, and a synchronous demodulator 8 for subjecting the electrical signal to synchronous demodulation using the modulation waves as reference waves.
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