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Understanding Coherence Time in Light

What is Coherence Time?

The coherence time is a measure used in coherence theory to quantify the temporal coherence of light. It is defined as the time over which the field correlation function decays.

Complex Degree of Temporal Coherence

The complex degree of temporal coherence can be defined as the ratio of the field correlation at two different times to the field autocorrelation at a single time.

Calculating Coherence Time

The coherence time can be determined by integrating the square of the coherence function over all time delays. In the case of exponential decay, it is the time at which coherence decreases to about 37% of its initial value.

Coherence Length

Coherence length is the product of coherence time and the speed of light in a vacuum, used to quantify temporal coherence.

Relation to Linewidth

Coherence time is closely related to the linewidth of light. In the case of exponential coherence decay, the linewidth is inversely proportional to the coherence time.

Applications of Coherence Time

Laser systems, especially solid-state lasers, can exhibit long coherence times, which are crucial for various applications in fields like optical frequency metrology and coherence-related studies.

Understanding coherence time is essential for characterizing the temporal properties of light and plays a significant role in various scientific and technological applications.

Source: National Institute of Standards and Technology
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