Optical pulse
= Optical pulse
{title2=$\tau$}
An optical pulse is a finite-duration envelope of <light>. A nearly monochromatic pulse has many carrier oscillations within its duration $\tau$: in units with light speed one, its <wavelength> obeys $\lambda\ll\tau$. A slowly varying propagation-time map stretches the pulse duration by its derivative and divides the observed <frequency> by the same factor.
// Target: general-relativity.bigb