Stimulated emission

This is also called stimulated emission. When light (electromagnetic waves) is incident on an atom (molecule) in an excited state, the frequency of the light, ν, and the energy difference between the excited state ( E ₁ ) and the lower energy state ( E ₂ ) to which it can transition by emitting light are

ΔE ₌ E1 _- E2
Between

Δ E ＝ hν
When this relationship is satisfied, the action of light (electromagnetic waves) causes atoms (molecules) to emit light with the same frequency, polarization component, and direction of travel as the incident light, and transition to a lower energy state. This is called stimulated emission. The probability of stimulated emission is proportional to the intensity of the incident light (number of photons), and is also related to the strength of the interaction between the light and the atom. This stimulated emission is the opposite phenomenon to light absorption, and its probability is exactly the same. Needless to say, in addition to stimulated emission, atoms (molecules) in an excited state can also emit light even in the absence of incident light, and this is called spontaneous emission.

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

誘導放射ともいう．原子(分子)が励起状態におかれているときに光(電磁波)が入射すると，光の振動数νと，励起状態(E₁)とそれから光の放出による遷移が可能な低エネルギーの状態(E₂)との間のエネルギー差

ΔE ＝ E₁ － E₂
との間に，

ΔE ＝ hν
の関係が満たされると，光(電磁波)の作用により原子(分子)は入射した光と同じ振動数，偏光成分，進行方向の光を放出して低エネルギーの状態に遷移する．これを誘導放出という．誘導放出を行う確率は入射する光の強度(光子の個数)に比例し，また光と原子の相互作用の大きさに関係する．この誘導放出は光の吸収の逆の現象であって，その確率はまったく同じである．いうまでもなく，励起状態にある原子(分子)は誘導放出以外に，入射する光が存在しなくても光を放出することが可能で，これは自然放出とよばれる．

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