A grating is an optical element composed of a series of equidistant parallel grating lines. It is a dispersive element that uses the principle of light diffraction and interference to split light. It is widely used in biochemical instruments, spectrometers, spectrophotometers, and other related products. In related fields. There are two types of gratings: transmissive and reflective. Reflective gratings are often applied to spectrometers. Each slot of equal width and parallel has the function of an optical slit. There will be 1200, 1800, 2400 lines per millimeter And so on, there will be hundreds of thousands of engraved lines on the whole grating, which can effectively split the light. In general reflective gratings, the main pole of zero-order diffraction, which has no chromatic dispersion ability in the grating diffraction, occupies 80% of the diffracted light intensity. As the main pole is increased, the light intensity becomes weaker, so the line groove is carved into a zigzag shape Make it have the ability to directional blaze so that the ability can be concentrated in the required wavelength range. From the manufacturing method, it can be divided into ruled gratings and holographic gratings. The ruled gratings are made by the marking machine on the reflective surface, and the holographic gratings are made by laser interferometry.
Transmission grating
The optical path design of the transmission grating is simple. For applications that use a fixed grating, the transmission grating has obvious advantages, such as a spectrometer. The incident beam is dispersed at a fixed angle on the back of the grating. Transmission gratings are not sensitive to some types of grating collimation errors. In order to obtain high diffraction efficiency, the density of transmission grating lines is not high. The diffraction angle will increase with the increase of the reticle density, and the refractive index of the base material limits the long-wave transmittance, resulting in performance degradation. The dispersion characteristics of gratings make them suitable for compact systems using small detector arrays. Such gratings are not sensitive to polarization.
Transmission grating beam splitter
The transmissive grating beam splitter is usually used for the splitting of He-Ne laser beams and the separation of multiple lasers in the visible range. The transmitted light beam is diffracted into multiple orders. The transmission grating beam splitter is composed of an epoxy resin replication layer plated on a polished glass substrate that matches the refractive index to obtain a higher total diffraction efficiency. These beam splitters are specifically designed for He-Ne laser beam splitting.
Planar engraved lines diffraction grating
The initial step of making the original or master grating is the choice of substrate material, usually glass or copper. Polish the base material to a high level of flatness and coat it with a thin aluminum film. It takes a long time to adjust the parallelism of the scribing and the equidistance of the scribing. It may take a few days to set up and test before the actual scribing. The scoring machine must be able to fold back the diamond head according to a precise route after each scoring, and score the substrate by a predetermined amount. The parallelism and displacement of the engraved lines must be precisely controlled.
Planar holographic grating
Holographic gratings are commonly used in applications that are sensitive to stray light. The base is plated with a photosensitive material, and the substrate coated with the photosensitive material is placed between the intersecting beams composed of monochromatic light and coherent beams generated by the laser, so that the photosensitive material is exposed to light. The intersecting laser beams produce a series of parallel and equidistant interference fringes, and the fringe intensity changes according to a sinusoidal shape. Since the solubility of the photosensitive material is determined by the light intensity irradiated to it, the interference fringes show different light intensities on the surface of the photosensitive material. The substrate can then be coated with a reflective film and then replicated using the same process as the original grating scribed. Because the holographic grating’s ruled line shape and pitch are completely consistent, the stray light generated is far less than that of a ruled grating. Holographic gratings can use two groove profiles, sinusoidal and blaze.
