Reflection ↑ n s, ↑ R Reflectivity varies with wavelength Typical silicate glasses: Reflection losses for lenses: coating surface with very thin layers of dielectric materials Example: MgF 2 Ībsorption Nonmetals: Opaque Transparent If transparent, often colored Reflection If light is normal to the interface: n 1 and n 2 are indices of refraction of the 2 media The larger the atom/ion: ↑ electronic polarization, ↓velocity, ↑n Refraction Crystalline ceramics: Glasses and cubic crystal structures: isotropic n Noncubic: anisotropic n n for some transparent materials Index of refraction:, = velocity in a medium = velocity in vacuum Refraction When light enters a material and its velocity decreases, it becomes bent at the interface. Optical Properties of Nonmetals Nonmetallic materials may absorb, reflect, refract or transmit light depending on their electron energy band structures Gold is gold because some of the energy associated with light photons having short wavelengths is not reemitted as visible light. Silver and Gold Silver is silver because when it is exposed to white light, it reflects almost all of the light.
Some small fraction of the energy from electron decay processes is dissipated as heat. Highly reflective metals The reflectivity for most metals is between 0.90 to 0.95. When electrons absorb light, they jump to a higher empty energy level or empty states. Why is silver silver? Why is gold gold? Īll frequencies of visible light are absorbed by metals because of the continuously available empty electron states, which permit electron transitions. Most of the absorbed radiation is reemitted from the surface in the form of visible light of the same wavelength, which appears as reflected light. Optical Properties of Metals Metals are opaque and highly reflective.