English: Brendel-Bormann oscillator model. The real (blue dashed line) and imaginary (orange solid line) components of relative permittivity are plotted for a single oscillator model with parameters ${\displaystyle \omega _{0}}$ = 500 cm${\displaystyle ^{-1}}$, ${\displaystyle s}$ = 0.25 cm${\displaystyle ^{-2}}$, ${\displaystyle \Gamma }$ = 0.05 cm${\displaystyle ^{-1}}$, and ${\displaystyle \sigma }$ = 0.25 cm${\displaystyle ^{-1}}$.