B What is the underlying reason for stimulated emission?

[physics loverq]

I learned that stimulated absorption, spontaneous emission and stimulated emission are three fundamental concepts in the process of radiation. Among these three concepts, I found stimulated emission really hard to comprehend, it says when atom in its excited state is stimulated by external photon, then the photon emitted by the atom when jumping to ground state will have the SAME wave-vector, phase, and polarization with external stimulating photon. Don't you think it's weird? why the emitted photon can't have different phase and polarization from stimulating photon(which should be more natural thing to happen)?

Actually,I have this problem haunting in my mind for a very long time, does anyone here know the answer? or any references to recommend? Both papers and treatises are okay. Really thanks for your help.

 

[BvU]

It's a matter of resonance. You must have googled a lot already; a text on quantum electronics will probably be more appropriate than a QED treatment by a theoretician, but then again... real experts might beg to differ

Christopher Davis at UMD has a http://www.ece.umd.edu/~davis/C1.pdfhttp://www.ece.umd.edu/~davis/ENEE496.html with C1 on SE (figures missing, unfortunately)
http://www.springer.com/cda/content/document/cda_downloaddocument/9783319051277-c1.pdf?SGWID=0-0-45-1448603-p176584453

All from googling 'quantum electronics spontaneous and stimulated emission in laser pdf' which you can do yourself, I suppose ?

 

[physics loverq]

It's a matter of resonance. You must have googled a lot already; a text on quantum electronics will probably be more appropriate than a QED treatment by a theoretician, but then again... real experts might beg to differ

Christopher Davis at UMD has a http://www.ece.umd.edu/~davis/C1.pdfhttp://www.ece.umd.edu/~davis/ENEE496.html with C1 on SE (figures missing, unfortunately)
http://www.springer.com/cda/content/document/cda_downloaddocument/9783319051277-c1.pdf?SGWID=0-0-45-1448603-p176584453

All from googling 'quantum electronics spontaneous and stimulated emission in laser pdf' which you can do yourself, I suppose ?

Really appreciate your help, I'll search that online and read the article shared by you. Thanks again.

 

[Cthugha]

[...], I found stimulated emission really hard to comprehend, it says when atom in its excited state is stimulated by external photon, then the photon emitted by the atom when jumping to ground state will have the SAME wave-vector, phase, and polarization with external stimulating photon. [...]

The phase part is actually a common myth. The phase of stimulated emission is 90 degrees in lead of the driving field. This is also necessary to have conservation of energy. This quite recent manuscript from Optica (should be open access and: yes, the wording in the spontaneous emission part is bad) shows for example how this can be understood even in a semiclassical picture:
https://www.osapublishing.org/optica/abstract.cfm?uri=optica-5-4-465

The full reference would be: Optica 5, 465-474 (2018). There are also references to experiments showing this phase difference within the manuscript.

 

[sophiecentaur]

The phase part is actually a common myth. The phase of stimulated emission is 90 degrees in lead of the driving field.

Ah yes - the phase doesn't matter in a laser; it's just the frequency that has to be the same.