Lifetime broadening ($\Delta {\omega }_{\mathrm{FWHM}}=1/T_1$)

In the absence of additional dephasing, a transition whose excited-state population has lifetime $T_1$ has a field-coherence decay time $2T_1$. Its Lorentzian line shape has angular-frequency half-width $1/(2T_1)$ and full width $1/T_1$. Population decay time, amplitude decay time and linewidth conventions must therefore be distinguished. Extra dephasing shortens the optical coherence time without necessarily changing the population lifetime.