May 6 2014
Optical flats can be described as an optical grade glass, which is polished and made extremely flat on both surfaces. They are used for determining the flatness of various optical surfaces. Optical flats determine the flatness of surfaces by interference.
Optical flats are usually disc shaped with parallel, or nearly parallel, surfaces, one of which is given an optical finish. Materials used for optical flats need to have a very small coefficient of thermal expansion.
This article will look further into the working, construction, and applications of optical flats.
Working Principle
Interference is the principle behind the working of optical flats. An optical flat is placed on a surface, in order to measure its flatness, before a monochromatic light is made to pass through the area of contact.
In cases where the test surface is perfectly flat, there will be no gap between the two surfaces. In cases where the test surface is not flat, interference fringes will be formed, and will be visible in the form of dark and light bands.
The elevation of the surface is determined by counting the fringe differences.
Construction
Most optical flats are made out of quartz. Some are made out of glass. Optical flats made of quarts are often coated on one side, to give higher reflectivity. Optical flats are in the shape of discs, having parallel surfaces.
Applications
The main applications of optical flats are listed below:
- Calibration of flatness of various optical surfaces
- Inspection of gauge blocks
- Testing of filters, mirrors, and prisms
- Spectrophotometry
References