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If I want to pump Rubidium 87 atoms From fg = 2 to fe=1 level with a laser tuned to D1 transition and avoid stimulated emission then it is sufficient that I use a laser power which gives me an instensity less than saturation intensity (Isat)

If my laser emitter diameter is 4 micron, then my laser power should be less than Isat * emitter area

Note: When laser intensity equals Saturation intensity, excited state atoms are equally likely to decay by stimulated emission or by spontaneous emission

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  • $\begingroup$ So what's the question? $\endgroup$ Jun 25, 2015 at 13:24
  • $\begingroup$ What does "fg" and "fe" stand for? You should exactly specify which state $|J,I,F\rangle$ you are considering. $\endgroup$
    – dolun
    Jun 25, 2015 at 14:34

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You can not avoid stimulated emission! This is a fundamental mechanism that has a certain likelihood depending on the intensity of the pumping laser light. However as you say, as long as the lasing threshold has not been reached this likelihood is very small and most of the radiation is done under spontaneous emission. The ratio of the likelihood of spontaneous emission over stimulated emission can be assessed from Einstein coefficients. However I am not 100% sure that these 2 likelihoods become equal at threshold(not saying it is not the case though). It would be great if you could give me a proof of that

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