Michelson Interferometer – Interference Fringes
The intensity of the interference fringes for a Michelson interferometer is given by
where I1 and I2 are the intensities of the two beams, λ is the wavelength, and d is the path length difference between the two interferometer arms. x and y are coordinates in the focal plane of a lens of focal length f.
The fringes for wavelengths λ = 632.8 nm and 420 nm are shown below. Note that as the magnitude of the path difference increases the fringes move outward while as the magnitude of the path difference decreases the fringes move inward.