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I have a laser beam whose power I measured to be x $\text{mW/cm}^2$. Furthermore, I measured the beam profile of the laser beam and therefore can estimate its intensity. I shine this laser through a vapour cell filled with Rubidium atoms and after it passed the vapour cell let it reflect by a mirror and pass through the vapour cell again (perfectly collinear). Will the laser power/intensity inside my vapour cell be doubled since there are now effectively two laser beams? Or will there just form a standing wave and the power/intensity are unaffected?

This is relevant since, e.g., the scattering rate in Doppler cooling requires knowledge of the laser intensity "as perceived by the atoms".

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In short it depends on the coherence of the laser and the path length. Its basically a michleson interferometer.

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  • $\begingroup$ And how would I be able to determine if this is the case in my setup or not? The total path length from laser source/Faraday isolator to aforementioned mirror are several meters. I don't have any particular knowledge regarding the coherence of my laser. $\endgroup$ – Lenus Stueli Jun 21 at 7:11
  • $\begingroup$ You probably will be on and it will just be double the irradiance. You could measure it with a beam pick off and a power meter. $\endgroup$ – MJC Jun 21 at 7:25

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