Table of Contents
What is Interferometer – michelson interferometer
1. Types of light sources and interferometer
(A) Types of light sources
A wide varieties of light sources are available for interferometer. The selection of proper source for an application depends on the result to be obtained by interferometer cost and convenience. For simple applicating like testing of surface geometry where the different between the interfering path is of the order of few wavelengths only a tungsten lamp with a filter transmitting only a narrow band of wavelength would be adequate.
However sophisticated application requires the use the light sources such as mercury 198 cadmium krypton thallium helium hydrogen neon sodium potassium zinc laser radiation etc. in these sources the discharge lamp is charged with the particular element and contains means to vaporize them. The atoms of these elements are excited electrically so that they limit radiation at certain discrete wavelength.
(B) Interferometer & types of interferometers
Interferometers are optical instrument used for measuring flatness and determining the length of slip gauges. They are based upon the interference principle and employ wavelength of light as their measuring units. The interferometers make use of some type of beam deliver that splits an incoming ray into 2 parts as shown in fig . the 2 parts of the ray travel along different parts until they are recombined.
In interferometers the lay of optical system can be controlled and the fringes can be oriented to the best advantage. Secondly an arrangement to view the fringes directly from top and above the fringes is also in corporate.
Types of interferometer
The various types of interferometers are:
(1) Michelson interferometer
(2) Fabre parrot interferometer
(3) Fringe counting interferometer
(4) N.P.L flatness interferometer
(5) Pitter NPL gauge interferometer
(6) Zeiss gauge block interferometer
(7) Multiple beam interferometer
(8) Laser interferometer
This is the oldest type of interferometer. It which is monochromatic light from an extend source. The monochromatic light falls on a beam splitter as shown in fig . the beam splitter is a lain parallel plate having a semi transparent layer of silver at its back. It has 50% reflectance. It splits the light into two rays of equal intensity at right angles. One is transmitted through compensating plate to the mirror and the other
reflected through beam splitter to mirror m. from both these mirror the rays are reflected back and these reunite at the semi reflecting surface from where they are transmitted to the eye as shown in fig . as a result of which the fringes can be observed. The mirror m is fixed whereas the mirror m is movable i.e it is attached to the object whose dimension is to be measured.
Each half wavelength of mirror travel produces a change in the measured optical path of one wavelength and the reflected beam from the moving mirror shifts through 360 phase change. When the reference beam reflected from fixed mirror and the beam reflected from moving mirror rejoin at the beam splitter, they alternately rein force and cancel each other as the mirror moves. Thus each cycle of intensity at the eye represents distance of mirror travel.
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