Coherence time

For an electromagnetic wave, coherence time is the time over which a propagating wave (especially a laser or maser beam) may be considered coherent. In other words, it is the time interval within which its phase is, on average, predictable.

Additional recommended knowledge

Correct Test Weight Handling Guide: 12 Practical Tips

Weighing the right way

What is the Correct Way to Check Repeatability in Balances?

In long-distance transmission systems, the coherence time may be reduced by propagation factors such as dispersion, scattering, and diffraction.

Coherence time, τ, is calculated by dividing the coherence length by the phase velocity of light in a medium; approximately given by τ = λ² / (cΔλ) where λ is the central wavelength of the source, Δλ is the spectral width of the source, and c is the speed of light in vacuum.

See also

• Coherence length
• Laser

References

• Federal Standard 1037C
• MIL-STD-188