Temporal Coherence

Temporal coherence

Temporal coherence is the measure of the average correlation between the value of a wave and itself delayed by ${\displaystyle \tau }$, at any pair of times. Temporal coherence tells us how monochromatic a source is. In other words, it characterizes how well a wave can interfere with itself at a different time. The delay over which the phase or amplitude wanders by a significant amount (and hence the correlation decreases by significant amount) is defined as the coherence time${\displaystyle \tau _{\mathrm {c} }}$. At a delay of ${\displaystyle \tau =0}$ the degree of coherence is perfect, whereas it drops significantly as the delay passes ${\displaystyle \tau =\tau _{\mathrm {c} }}$. The coherence length${\displaystyle L_{\mathrm {c} }}$ is defined as the distance the wave travels in time ${\displaystyle \tau _{\mathrm {c} }}$.