The optical flat should usually never be allowed to fully wring to the surface, otherwise it can be scratched or even broken when separating them.
12.
These interference fringes determine the flatness of the work piece, relative to the optical flat, to within a fraction of the wavelength of the light.
13.
The lower section shows how the ? / 4 harmonic interacts in visible light ( green and red ), as photographed in an optical flat . ]]
14.
To provide an even flatter surface, sometimes the test may be performed on top of another optical flat, with the test surface sandwiched in the middle.
15.
Testing flatness with an optical flat is typically done as soon a viable interference pattern develops, and then the surfaces are separated before they can fully wring.
16.
Optical flats are sometimes given an optical coating and used as precision mirrors or optical windows for special purposes, such as in a Fabry P�rot interferometer or laser cavity.
17.
"' Clear filters "', also known as window glass filters or optical flats, are transparent and ( ideally ) perform no filtering of incoming light.
18.
The fringes only appear in the reflection of the light source, so the optical flat must be viewed from the exact angle of incidence that the light shines upon it.
19.
However, if the optical flat is rotated 90 degrees and retested, the fringes will run perpendicular to the valley and it will show up as a row of " V " or " U " shaped contours in the fringes.
20.
Flatness and parallelism are typically measured with a gauge called an optical flat, a disc of glass or plastic ground with extreme accuracy to have flat, parallel faces, which allows light bands to be counted when the micrometer's anvil and spindle are against it, revealing their amount of geometric inaccuracy.
