Brechungsindexbestimmung

The Brechungsindex, or refractive index, of a medium quantifies how light propagates relative to vacuum. It is the phase velocity ratio c/v and is related to the ratio of electromagnetic wave impedances. In many contexts, n is wavelength-dependent and can vary with temperature and composition.

When light crosses an interface between two media, n1 sin theta1 = n2 sin theta2 (Snell's law). Measurements use prism refraction, refractometry, and fiber-optic sensing. Common approximate values: air around 1.0003, water around 1.333, glass around 1.5.

Most materials exhibit dispersion: n varies with wavelength, producing prism color separation. Models such as the Sellmeier or Cauchy equations describe this dependence for visible light and other ranges. Dispersion is essential in lens design, coatings, and optical communication.

In anisotropic crystals, light can propagate with different refractive indices for ordinary and extraordinary rays, a phenomenon called birefringence. For absorbing media, the refractive index is complex, n = n' − i k, where k describes attenuation.

Refractive index relates to dielectric properties through n^2 ≈ ε_r μ_r; for non-magnetic materials μ_r ≈ 1, so n ≈ sqrt(ε_r). It is central to imaging, fiber optics, and sensors; environmental factors such as temperature, pressure, and composition influence its value.