What are the advantages of measuring weak vibration displacement with double gratings?

The optical element that uses the principle of multi-slit diffraction to disperse light (decompose it into spectrum) is that a large number of parallel equal-width and equidistant slits (scribes) are engraved on the plane glass or metal plate. The number of slits in the grating is very large, generally tens to thousands per millimeter.

The diffraction of monochromatic parallel light through the slits of the grating and the interference between the slits form patterns of wide dark stripes and thin bright stripes, which are called spectral lines. The position of the spectral line varies with the wavelength. When polychromatic light passes through the grating, spectral lines with different wavelengths appear in different positions, forming spectra. The spectrum formed by light passing through grating is the same result of single-slit diffraction and multi-slit interference.

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Precision measurement has always played an important role in the field of automation control, among which photoelectric measurement is often used in measurement applications because of its good precision and accuracy, portability and no noise. As a means to convert mechanical displacement signals into photoelectric signals, grating displacement measurement technology has been widely used in digital measurement of length and angle, comparative measurement of motion, numerical control machine tools, stress analysis and other fields.

Because the medium has different phase delay effect on the propagation of light, if two beams of the same monochromatic light have the same initial phase, they pass the same geometric path, but they propagate in different refractive index media, then the phases of the two beams of light are different.

Baidu Encyclopedia-Double Grating Weak Vibration Measuring Instrument