Homogeneous spectral broadening ($\Delta {\omega }_{\mathrm{FWHM}}=2/T_2$)

Broadening shared by otherwise identical emitters, often described by a common optical coherence time $T_2$. Exponential field-coherence decay produces a Lorentzian line shape with full angular-frequency width $2/T_2$. Population decay, dephasing and collisions can all contribute, with their time constants distinguished.