Page "Michelson interferometer" Paragraph 3

In Fig 2, a source S emits light that hits a beam splitter ( in this case, a half-silvered mirror ), surface M, at point C. M is partially reflective, so one beam is transmitted through to point B while the other is reflected in the direction of A.

Both beams recombine at point C ' to produce an interference pattern ( assuming proper alignment ) visible to the observer at point E. To the observer at point E, the effects observed would be the same as those produced by placing surfaces A and B ' ( the image of B on the surface M ) on top of each other.

Fig.

2 shows use of a monochromatic source.

White light can also be used, provided that the path lengths are carefully equalized, a requirement due to the short coherence length of white light ( on the order of a micron ).