| 摘要 |
According to one embodiment, a displacement detection device includes a light source, objective lens, beam splitter, aperture limiting element, and detection device. The beam splitter may separate reflected light into portions. The reflected light may be reflected by the medium and then transmitted through the objective lens. The aperture limiting element may include an aperture limited so as to block a portion of the reflected light. The detection device may detect displacement of the medium in a direction of the optical axis based on the reflected light having passed through the aperture limiting element.
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