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Measurements Applications
Measuring Coherence Length
Alpha factor
The alpha factor is defined as the height of the first envelope peak away from
zero path delay relative to the height of the envelope peak at zero path delay.
The alpha factor is always between 0 and 1.
The
smaller
the alpha factor, the shorter the coherence length.
Beta factor
The beta factor is defined as the height of the fringe visibility envelope mid-
way between the zero optical path delay peak and the next peak relative to the
height of the envelope peak at zero path delay. The beta factor is always
between 0 and 1.
The
smaller
the beta factor, the more longitudinal modes (wavelengths) the
laser has.
Alpha factor
V
A
V
o
------=
Beta factor
V
B
V
o
------=