The main function of transmission grating is to disperse composite light, that is, to separate light of different wavelengths. It is made by carving a series of equal width and equal spacing into a very flat piece of glass, where the score is equivalent to ground glass, most of the light will not pass through, and between the two nicks is equivalent to a slit, allowing light to pass through.

Transmission grating is widely used in spectral analysis. It can be used to measure information such as the wavelength and intensity of light waves, thereby helping scientists understand the composition, structure and properties of matter. It can also be used for optical instruments, such as spectrometers, monochromators, etc., to improve the accuracy and performance of the instrument

The principle of formation is moire fringe. The long grating and the short grating are overlapped, and the gap between them is 0.01mm-0.1mm, and the lines of the two grating are rotated by a small Angle. When the light shines parallel to the grating, due to the transmission and diffraction effect of the light, in the direction perpendicular to the line, precisely, in the direction perpendicular to the bisector line of the Angle θ between the two grating lines, there will be alternating thick stripes with equal intervals, which is "Moire interference stripes", referred to as Moire stripes. The distance between two bright or two dark bands is called the spacing B of the Moire fringe. If the grating distance of the grating is W and the Angle between the two grating lines is, then the following geometric relationship exists between them:

Because theta is small, so

B = W / Θ

Linear transmission grating is composed of ruler grating, indicator grating, light source, lens, photoelectric element and detection circuit. Ruler grating and indicator grating can also be called long grating and short grating, respectively, and their linear density is equal. The long grating can be installed on a fixed part of the machine (such as the machine bed), the length of which is selected to be the full stroke of the machine table. The short grating is mounted on the moving parts of the machine (such as the table). When the table moves, the indicating grating moves relative to the scale light shed. The two grating scales overlap with each other in parallel, and maintain a certain gap, and the two planes turn a small Angle relative to each other. In practical applications, the light source, indicating grating and photosensitive elements are always combined together, which is called the reading head. Therefore, the grating position detection device can be regarded as composed of two parts: reading head and ruler grating.

Diffraction grating can propagate light of different colors (wavelengths) in space according to certain rules, which is due to the diffraction and interference phenomena that occur when the light passes through the grating.

In the spectrometer, with diffraction grating as the core component, the composite light can be decomposed into monochromatic light, so as to carry out quantitative and qualitative analysis of substances, such as the characteristics of light source, solution concentration, biological effects of light, optical properties of transparent substances, etc.

In inertial confinement fusion experiments, laser pulses are compressed to very short pulse widths using diffraction gratings and fusion reaction processes are detected.

In the field of laser processing, diffraction grating is used to produce high quality laser beam and improve processing accuracy and efficiency.

In astronomical research, diffraction gratings are used to analyze the spectrum of light emitted by stars and other celestial bodies to obtain information about their chemical composition, temperature, density, and so on.

Diffraction gratings play a role in precision measurements, such as length measurement and Angle measurement, and high-precision measurements can be made using the grating's precise splitting ability.

In optical fiber communication system, diffractive grating is used to split beam and beam to realize signal transmission and modulation.

Diffraction gratings are also used in augmented reality (AR) technology to generate virtual images and overlay them onto the real world.

To sum up, diffraction gratings have been widely used in many fields, and their high resolution and accurate spectral splitting ability make them an indispensable tool in modern science and technology.

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