Fringes in N.P.L. Interferometer - Metrology & Quality Control

Q.  Which among the following is used to create fringes in N.P.L. interferometer?
- Published on 07 Aug 15

a. Condensing lens
b. Collimating lens
c. Optical flat
d. All of the above

ANSWER: Optical flat


  • Sravanthi   -Posted on 26 Oct 15
    - Optical flat is placed below the collimating lens. This optical flat produces fringes. The fringes obtained are viewed through a thick glass plate reflector which is set at an angle of 45° to the optical axis.

    - Optical flat is an optical grade which is glass lapped and polished to have flat surfaces on both the sides. Flatness of optical surfaces by interferences is obtained by using optical flat with a monochromatic light.

    Whenever an optical flat is placed on other surface and illuminated, light waves from bottom and surface are reflected. This gives rise to a phenomenon same as thin-film interference.

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