There are many types of optical glass, and filter is one of them, which can change the direction of light propagation. Filter is an optical device used to select the desired radiation band. As an optical device, it is a part of the development of the optical industry, and there are requirements for the surface smoothness, transmittance, reflectivity, accuracy of product parameters, and cut-off depth of the filter. Filters are used in lenses, prisms, and other optical instruments.
Filters are generally divided into two categories:
1. Color filter, which is a flat glass or gelatin sheet of various colors with a transmission bandwidth of several hundred angstroms.
2. Thin film filters can be divided into two types: thin film absorption filters and thin film interference filters.
The former is achieved by chemically etching a specific material substrate to position the absorption line precisely at the desired wavelength. Generally, it has a longer wavelength and is often used as an infrared filter. The latter is composed of metal dielectric metal films or fully dielectric films with a certain thickness of refractive index or low refractive index alternately formed by vacuum coating on a certain substrate.
The main characteristic of a filter is that its size can be made large. Thin film filters, typically with long wavelengths, are commonly used as infrared filters. The latter is a low-level, multi-stage series solid Fabry Perot interferometer formed by alternately forming metal dielectric metal films or all dielectric films with a certain thickness of refractive index or low refractive index on a certain substrate using vacuum coating method. The selection of material, thickness, and series connection method for the membrane layer is determined by the required center wavelength and transmission bandwidth λ.
Where are the applications of filters in our daily lives generally reflected?
1. Applied to the photography industry
Photographers always use filter technology to highlight a certain person or scenery during filming, making the landscape presented to the audience clear at a glance.
2. Applied to testing instruments and other equipment
Filters can also project and reflect incoming light in a certain proportion. So that these detection instruments can play different roles in various aspects. Some instruments require strong light, while others require weak light, which requires different filters to allow them to continue operating.