Question

Why do we need external radiation for releasing energy in stimulated emission?

Answer 1

When an electron absorbs energyeither from light (photons) or heat (phonons), it receives that incident quantum of energy. ... When such an electron decays without external influence,emitting a photon, that is called "spontaneous emission". The phase and direction associated with the photon that is emitted israndom.

Answer 2

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Stimulated emission is the process by which an incoming photon of a specific frequency can interact with an excited atomic electron causing it to drop to a lower energy level.

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