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# Optical properties

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## Oscillator Options

 ε∞:

Oscillator 1

 ω0 [cm-1]: ωP [cm-1]: γ [cm-1]:

Oscillator 2

 ω0 [cm-1]: ωP [cm-1]: γ [cm-1]:

Oscillator 3

 ω0 [cm-1]: ωP [cm-1]: γ [cm-1]:

Oscillator 4

 ω0 [cm-1]: ωP [cm-1]: γ [cm-1]:

Oscillator 5

 ω0 [cm-1]: ωP [cm-1]: γ [cm-1]:
Blue shows the real part of the function, red the imaginary part. Click on the graph to zoom in!
© II. Physikalisches Institut, Universität zu Köln / University of Cologne

# Instructions

1) What does the applet show?

The applet visualizes an oscillator model (Drude-Lorentz model) for the dielectric function, which is the central quantity for the description of the frequency-dependent optical properties of solids. In insulators and metals, an oscillator may e.g. describe an infrared-active optical phonon mode. The contribution of free carriers in a metal (Drude model) can be described by setting the resonance frequency omega_0 of one oscillator equal to zero.

The dielectric function is shown as a function of frequency omega (in units of "wavenumbers" 1/cm, i.e. inverse wavelength 1/lambda) in the upper left panel. The dielectric function is a complex function, so the real part is displayed in blue an the imaginary part in red. Other complex optical quantities which can be derived from the dielectric function are the optical conductivity sigma(omega) (lower left panel) and the complex refractive index N = n + i*k (bottom right panel; blue: real part, red: imaginary part). The upper right panel shows the reflectivity R(omega).

2) How to use the applet?

The oscillator model assumes that the dielectric function is described by a sum of "oscillators". The user may modify the number of oscillators and the parameters of each oscillator. Each oscillator can be modified using the following adjustments:
- change the resonance frequency omega_0
- change the plasma frequency omega_p (a measure of the oscillator strength)
- change the damping gamma (a measure of the width)
All three parameters are given in units of wavenumbers. Additionally, the user may vary "epsilon infinity", which is a constant offset for the real part of the dielectric function. Epsilon infinity sums up all contributions lying at much higher frequencies and also contains the contribution of vacuum (i.e, 1).