In LASERS, when the initial stimulated photon gets emitted, it stimulates other photons to get emitted. Now my question is: Does the wave of this photon interfere with other waves and makes a bigger amplitude wave or we get two waves of same frequency and in same phase?

If we get two waves of same frequency and in same phase, what is the reason for having both waves in phase.isn't the first wave had just stimulated other atom to de excite? Why the new wave released should be in phase with wave stimulated its release(or produced it in general sense). Is there any principal behind this phenomenon or is it just a practical observation. Thanks.


closed as unclear what you're asking by Sebastian Riese, AccidentalFourierTransform, garyp, CuriousOne, user36790 May 2 '16 at 3:29

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  • $\begingroup$ Waves are not something you can count. There can't be one wave or two waves. Photons you can count, but they do not correspond to classical waves – coherent states of photons do. But the central point of a laser is, that the photons are emitted coherently. The second part of the question does not make any sense, as the situation is not specified in sufficient detail. $\endgroup$ – Sebastian Riese May 1 '16 at 14:01

Regarding your 1st question, the two options you give appear to be the same. Using the wave picture, the emitted wave is in phase with the incident wave, and the two waves (which have the same frequency and are in phase) interfere constructively to make a wave of larger amplitude. The emitted wave is in phase with the incident wave because the excited atom is "stimulated" by it : it resonates in phase with it.

Regarding the gain, it is more like the former : 1 photon stimulates emission of a 2nd to make 1x2=2; each of these 2 stimulates emission of another 1 to make 2x2=4; each of these 4 stimulates emission of another 1 to make 4x4=16; etc. So the gain is exponential.

However this depends on there being plenty of excited atoms left to be stimulated. As more photons are emitted, there will be fewer excited atoms left. So the gain (rate of increase of photons) will fall.


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