Question

relation between coherence length and quality factor
​

Answer 1

Answer:

The temporal coherence time is the time the wave-fronts remain equally spaced. That is, the field remains sinusoidal with one wavelength: The spatial coherence length is the distance over which the beam wave-fronts remain flat: Since there are two transverse dimensions, we can define a coherence area.

Answer 2

Explanation:

The coherence length can be used for quantifying the degree of temporal (not spatial!) coherence as the propagation length (and thus propagation time) over which coherence degrades significantly, i.e., the optical phase undergoes substantial random changes. It is defined as the coherence time times the vacuum velocity of light.

For example, if the coherence length of a laser is 1 km, the phase relationship between two points along the laser beam, with a distance of 1 km between them, is still significant, but already substantially degraded by phase fluctuations of the laser.

Hope this will help you.