Refarctive index (absence of attenuation in vacuum)

Description

When an electromagnetic wave travels through a medium in which it gets attenuated (this is called an “opaque” or “attenuating” medium), it undergoes exponential decay as described by the Beer–Lambert law. However, there are many possible ways to characterize the wave and how quickly it is attenuated.

For a given frequency, the wavelength of an electromagnetic wave is affected by the material in which it is propagating. In the absence of attenuation, the index of refraction (also called refractive index) is the ratio of these two wavelengths.