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During stimulated emission in laser,the electron de-excites by supplying energy,generally it must excite,right? My doubt is then why does it de-excites?

Preeti Preeti
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    To nitpick a little: it's the entire atom that is in an excited state, not just the electron. Your premise is correct, though. Stimulated emission happens when an excited atomic state emits a photon after it was exposed to another photon of similar energy. The process can symbolically be written as $a^* + \gamma \to a + \gamma + \gamma$, where $a^*$ is the excited state with a higher and $a$ is a different state with lower energy. As to "why": Einstein made a congenial argument based on thermodynamics, see e.g. here: http://farside.ph.utexas.edu/teaching/qmech/Quantum/node119.html – CuriousOne Jun 21 '15 at 04:47
  • possible duplicate of Atomic Physics: stimulated emission – John Rennie Jun 21 '15 at 05:29
  • The question I've linked asks: Can someone explain the reason why the incoming photon stimulates the atom to emit a second one? To me it seemed more logic for the atom to absorb the photon and go an energy level up. So it's an exact duplicate of yours. – John Rennie Jun 21 '15 at 05:30

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