Dependence of the refractive index on density, temperature, and the wavelength of the incident light

The refractive index of dielectrics is a function of the density, temperature, and the wavelength of the incident light. The refractive index and material dispersion are determined by the plasma and the resonance frequencies. Physically, the forced oscillation of an induced dipole is driven by the light wave, vibrating in the plane perpendicular to the propagation direction of light. The incident light is absorbed at the resonance frequency. In this case, the induced dipole is transformed into independent neutral oscillator (atom). Yet, the forced oscillation of the dipole and the thermal motion of the atom have different vibration modes. Each mode carries out thermal energy. The incident light should overcome the thermal energy to excite the vibration modes of the dipoles. These features lead to the temperature-dependent plasma and resonance frequencies, and consequently yield the temperature-dependent refractive index and material dispersion. Moreover, the change of refractive index with temperature is found to relate with specific heat capacity. The proposed approach is applied for analyzing the refractive index of silica glass.