How is a photon responsible for de-excitation of an electron in higher energy state?
Instead of searching for a reason for stimulated emission, you should change your point of view. When we say quantum mechanics is a probabilistic theory, some part of its meaning is that if we have no reason to say something can't happen, then it has a non-zero probability to happen.
Stimulated emission is introduced to physics by Einstein. He considered it in his theory only because he didn't have a reason not to consider it. Study about Einstein's coefficients.
Whatever i read doesn't satisfy the view that something like Stimulated emission really occurs.
Its just 1 of every 1000000 atoms where it occurs,as said, and that too when photon interacts with an excited electron without transfer of any sort of energy or momentum. Then how if photon responsible for electron's de-excitation. Further, if its just 1 of every 1000000 then it is possible that during the time, the photon is passing the atom the electron gets de-excites at the same moment by itself and we think it is photon who did it?
Stimulated emission is the basic principle for lasers and masers.
That really requires QFT:
The scenario you're describing is in fact spontaneous emission happening accidentally when a photon is passing by. That's OK but the point is spontaneous emission is considered before!
Physicists like to have theories as general as possible and resort to further assumptions only if things are very hard in the general case. Here it will be a further assumption if we say the electrons just ignore the fact that a photon is nearby. To keep things general, its said that the electron does not ignore the photon's presence. But how does it react? Absorbing the photon and going to an upper level is an obvious reaction. But here, people say:"Hey, what if the electron reacts by going down and emitting another photon? Let's have a theory with that stuff and see what are we going to get!". And the theory proved to be a good one: we have lasers! That's because no one has problem with stimulated emission:There is no reason not to consider it and its in agreement with observations!
But laser requires that all the photons emitted are monochromatic, coherent and in phase. But all know is that photon interacted and photon emitted are the only two which possess these property. So the monochromaticity, coherency, and in phase characteristics should be in pairs rather than whole because we can't say that all photons coming to interact to excited electrons really are monochromatic, coherent, and in phase.
I think its better that you read this page!
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