Brendel–Bormann oscillator model

The Brendel–Bormann oscillator model is a mathematical formula for the frequency dependence of the complex-valued relative permittivity, sometimes referred to as the dielectric function.

The model has been used to fit to the complex refractive index of materials with absorption lineshapes exhibiting non-Lorentzian broadening, such as metals[1] and amorphous insulators,[2][3][4][5] across broad spectral ranges, typically near-ultraviolet, visible, and infrared frequencies.

The dispersion relation bears the names of R. Brendel and D. Bormann, who derived the model in 1992,[2] despite first being applied to optical constants in the literature by Andrei M. Efimov and E. G. Makarova in 1983.

These drawbacks inspired J. Orosco and C. F. M. Coimbra to develop a similar, causal oscillator model.

is obtained from the convolution of the two aforementioned oscillators in the manner of which yields where The square root in the definition of

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 = 500 cm , = 0.25 cm , = 0.05 cm , and = 0.25 cm .