Reflection hologram scale for optical displacement measurement has reflection scale formed on rear of transparent surface

摘要

The holographic grating (12) is formed of a photosensitive layer with interference fringes recorded as a diffraction grating, on the rear surface of a scale substrate (11). A metal reflection film is directly formed on the grating surface and this is covered by a protection surface (15). In use a transmission diffraction grating (3) passes a coherent light beam and divides it into two components. Photodiodes (4,5) detect the reflected beams to monitor displacement.