OpticalMedium

OpticalMedium gives refractive index and permittivity of a material.

It uses Sellmeyer formula to retrieve refractive index and permittivity
at specified frequency, wavelength or photon energy in eV.
The available materials are listed in the file 'sellmeyer.csv', which
can be easily edited to add more materials.

examples:
n = OpticalMedium('BK7').refractiveIndex(800, 'nm');
n = OpticalMedium('SF10').refractiveIndex(2, 'eV');
n = OpticalMedium('BK7').refractiveIndex(350, 'THz');
eps = OpticalMedium('BK7').permittivity(800, 'nm');
eps = OpticalMedium('BK7').permittivity(2, 'eV');
eps = OpticalMedium('SF5').permittivity(350, 'THz');

References:
Refractive index values are mainly taken from http://refractiveindex.info/
and from SCHOTT data sheets.