Coming up next is a type of light which brings
about another kind of characterisation of the various properties of light.
Coherent Light
Light can be further characterized by its degree of coherence. Coherence in close relation
to polarization and to monochromaticity which actually refers to the ability of a beam of
light to interfere with itself.
Coherence is
therefore an interferometric property of light.
Interference fringes are produced by light
sources using by means of a Michelson interferometer. When the two arms of the
interferometer is equal, they are clearest. As one arm is made longer, however, the
fringes will seem to constrast each other ass seemingly dip until they no longer appear
visible.
Unfiltered light from an incandescent source
will barely produce fringes under any circumstances. Light from a mercury arc lamp will
produce fringes over a range of one or two centimeters. On the other hand, light from a
continuous-wave gas laser has produced fringes at a distance of over 100 meters.
Therefore, light can be characterized by its degree of coherence or coherence length.
