What is the principle of optical instruments in measuring small distances?

Optical instruments use the principle of interference to measure small distances.

Optical instruments, such as interferometers, use the principle of interference to measure small distances. Interference occurs when two or more waves meet and combine. In the case of an interferometer, a beam of light is split into two paths, which are then recombined. The resulting interference pattern can be analysed to determine the difference in distance between the two paths.

One type of interferometer is the Michelson interferometer. It consists of a beam splitter, two mirrors, and a detector. The beam splitter splits the incoming beam of light into two paths, which are reflected off the mirrors and then recombined at the detector. The interference pattern at the detector is then analysed to determine the difference in distance between the two paths.

Another type of interferometer is the Fabry-Perot interferometer. It consists of two parallel mirrors, with a gap between them. Light enters the gap and is reflected back and forth between the mirrors. The interference pattern is then analysed to determine the distance between the mirrors.

Optical instruments are used in a variety of applications, such as measuring the thickness of thin films, detecting small vibrations, and measuring the distance between two objects with high precision. The principle of interference allows for extremely accurate measurements, with resolutions on the order of nanometers.