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The Material Class

This class defines the optical parameters for a given material. The optical parameters are defined via the complex refractive index or equivalently the complex permittivity. As a shorthand, we will refer to the real part of the refractive index as n, the imaginary part as k and the complex refractive index as nk. Similarly, the shorthand for permittivity is eps_r, eps_i and eps

There are multiple ways to initalise this class. Typically the objects of this class will be generated using the catalogue.

It can also be initalised in the following ways,

  • using the path to a file
  • using a constant value for n, nk, eps_r or eps.
  • using tabulated data for n, nk or eps
  • using a predefined model

Apart from the file path, these different definitions can be mixed and matched. For example a model or tabulated data for n, while taking a constant value for k.

A material is full defined when either both the real and imaginary parts of the refractive index or permittivity are defined, or alternatively a complex value for either refractive index or permittivity is defined.

Once a material has been fully defined, the refractive index or permittivity can be evaluated on a given spectrum. The spectrum can be wavelength, frequency, angular frequency or energy. For more information see Spectrum

import numpy as np
from dispersion import Material, Spectrum
mat = Material(fixed_n = 1.5) # k will be set = 0
spm = Spectrum( np.arange(380, 750, 10 ),
               spectrum_type= 'Wavelength',
               unit = 'nanometer')
nk_values = mat.get_nk_data(spm)
eps = mat.get_permittivity(spm)

Interpolation

If tabulated data is used to initalise the MaterialData, it will be automatically interpolated. The order of interpolation can be set by passing interp_order as a keyword to the MaterialData constructor. The order must be an integer. The default value is 1 (linear interpolation).

Extrapolation

Data can be extrapolated outside of the range in which it is defined. This should be done with great care, as extrapolated values may not even be qualitatively correct. However in circumstances where the material dispersion is very low, it may be practical to extrapolate the close to the spectrum of known values. Note that since the real and imaginary parts are extrapolated separately they must be independent of one another. Therefore, the material must be defined via separate real and imaginary parts, rather than via a complex value.

Extrapolation is achieved as follows,

new_spectrum = Spectrum(800., spectrum_type='Wavelength', unit='nm')
mat.extrapolate(new_spectrum, spline_order=2)

Due to extrapolation using splines, the results can vary greatly depending on the spline order used. For this reason it is recommended to verify the results of extrapolation before using the results for further calculations.

Removing Absorption

Sometimes it is useful to remove the absorption by setting the imaginary part of material data to a constant zero value. This can be achieved by,

mat.remove_absorption()

Note that this is only valid for data which have independent real and imaginary parts.

Full API

.. automodule:: material
                :members: