Law of photochemical equivalence

From a particle perspective, light with wavelength λ is

It can be thought of as a particle with an energy of 1000 times the energy of light. Here, ν is the frequency of light, c is the speed of light, and h is Planck's constant. A. Einstein stated that when a photochemical reaction occurs, "light absorption always takes place in the form of the absorption of one photon." This is called the law of photochemical equivalence. However, when laser light is used as the light source, two-photon absorption and multi-photon absorption occur, so the law must be extended to state that "light absorption takes place in the form of the absorption of one or several photons."

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

粒子的にみれば，波長λの光は，

のエネルギーをもった粒子と考えられる．ここで，νは光の振動数，cは光の速度，またhはプランク定数である．A. Einstein(アインシュタイン)は光化学反応が起こる場合，“光の吸収はつねに光量子1個を取り込む形で行われる”とした．これを光化学当量の法則という．しかし，レーザー光を光源とするときは，二光子吸収や多光子吸収が起こるので，法則を拡張し，“1個あるいは数個の光量子を取り込む形で行われる”とする必要がある．

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