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The principle behind interferometer is very simple. 1.When a light source with low optical bandwidth is used, the detector signal differs periodically when the difference in arm lengths is changed. Such a signal enables to do measurements with a depth resolution. 2.If the detector is a kind of camera and the surfaces monitored are smooth, the phase profile can be reconstructed by recording multiple images with various overall phase shifts. 3.A wavelength-tunable source (laser) can be used to record the detector signal for various optical frequencies. From such signals, the arm length difference can be unambiguously retrieved. 4.If one of the mirrors is tilted, an interference fringe pattern will be obtained. Any change in arm length difference will moven the fringe pattern as well.

A Michelson interferometer, uses a single beam splitter for separating and recombining the beams. If the two mirrors are aligned for perpendicular incidence, only one output will be accessible. If that optical feedback is unwanted, access to the second output will be required and the recombination of beams can occur at a different location on the beam splitter. Alternatively, mirrors at non-normal incidence can be used.

Ritesh you have missed out the most important point. I.e in Michelson interferometer, if the path length difference is non-zero, constructive or destructive interference can be achieved within a finite optical bandwidth.

Thank you so much for the answers guys