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In optics, the Ewald–Oseen extinction theorem, sometimes referred to as just "extinction theorem", is a theorem that underlies the common understanding of refraction. It is named after Paul Peter Ewald and Carl Wilhelm Oseen, who proved the theorem in crystalline and isotropic media, respectively, in 1916 and 1915. == Overview == An important part of optical physics theory is starting with microscopic physics—the behavior of atoms and electrons—and using it to ''derive'' the familiar, macroscopic, laws of optics. In particular, there is a derivation of how the refractive index works and where it comes from, starting from microscopic physics. The Ewald–Oseen extinction theorem is one part of that derivation (as is the Lorentz–Lorenz equation etc.). When light traveling in vacuum enters a transparent medium like glass, the light slows down, as described by the index of refraction. Although this fact is famous and familiar, it is actually quite strange and surprising when you think about it microscopically. After all, according to the superposition principle, the light in the glass is a superposition of: * The original light wave, and * The light waves emitted by each of the atoms in the glass. (Remember, light has an electric field that pushes atoms back and forth, which causes the atoms to emit dipole radiation.) Individually, each of these waves travels at the speed of light in vacuum, ''not'' at the (slower) speed of light in glass. Yet when the waves are added up, they surprisingly create ''only'' a wave that travels at the slower speed. The Ewald–Oseen extinction theorem says that the light emitted by the atoms has a component traveling at the speed of light in vacuum, which exactly cancels out ("extinguishes") the original light wave. Additionally, the light emitted by the atoms has a component which looks like a wave traveling at the slower speed of light in glass. Altogether, the ''only'' wave in the glass is the slow wave, consistent with what we expect from basic optics. A more complete description can be found in Classical Optics and its Applications, by Masud Mansuripur. A classic proof of the theorem can be found in Principles of Optics, by Born and Wolf.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ewald–Oseen extinction theorem」の詳細全文を読む スポンサード リンク
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