Optical parts 101: Diffraction grating

A diffraction grating is an optical element made by forming fine grooves at regular intervals on a glass substrate. When the diffraction grating is irradiated with light, the effect of the groove causes a diffraction phenomenon of the light, so that the incident light can be divided according to the wavelength. There are various types such as transmissive type, reflective type, and blazed type. Since each has a slightly different structure, the spectral performance is also different.

Since a diffraction grating can extract light of a specific wavelength, it is used in spectroscopes such as monochromators that emit light of a single wavelength and polychromators that emit light of a certain wavelength.

Usage of diffraction grating

The diffraction grating has fine grooves on its surface, and has the property of splitting the incident light for each wavelength. This property is used in devices that control the wavelength of light.

For example, it is used in spectroscopes such as monochromators that emit single wavelengths and polychromators that emit wavelengths of a certain width. It is also used in spectrophotometers for astronomical observations, various spectrophotometers in the field of natural science , manufacturing equipment for pharmaceuticals and chemicals, and quality control equipment.

Diffraction grating principle

According to DZOptics, a diffraction grating is made by depositing a metal such as aluminum on a glass substrate and engraving a large number of parallel lines of 15,000 to 30,000 for ultraviolet to visible light and 1,500 to 2,500 for infrared. Interference fringes occur when these grooves scatter the incident light. As a result, the incident light can be separated according to the wavelength.

Diffraction gratings are used in many spectroanalyzers because they have better light resolution compared to prisms and show equal dispersion at all wavelengths. Prism is made from optical glass and is dispersed by taking advantage of the fact that the refractive index differs for each wavelength of light. On the other hand, in a diffraction grating, the diffraction direction of incident light differs depending on the wavelength, and the light is dispersed.

There are original and replica diffraction gratings. Original diffraction gratings are difficult and expensive to make because they need to be made with particular precision. Since many replica diffraction gratings can be manufactured from the original diffraction grating, they are inexpensive and widely used.