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I am working currently on cosmic particles detection and I was wonder, if according to Mie theory or maybe another kind of theory, if a particle of PM2.5 which travel at 10km/s and cross a laser beam could it actually be detected by a photosensitive diode ? In this case there is scattering for sure but during a fraction of second and then the main problem I have is that speed, I cannot find my answer in current Mie theory publications.

Thank you your help.

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There are single-photon avalanche diodes if you are willing to spend the money on them, so the photodetector is surely not the limit for your problem and if they don't work, then you can always use a photomultiplier tube. Neither is laser power these days. Nothing prevents you from focusing a 10W visible laser into a focal spot of a few micrometers in diameter. The photon flux in such a scenario is on the order of 10^20/s. A particle moving through a 2um region at 10km/s spends roughly 2e-10s in the focus, which leads to a max. photon flux of still over 10^9 photons even for particles of 20% reflectivity. So now you have nine orders of magnitude to play with for reducing the laser power, enlarging the detection volume, optical system losses and the signal to noise of your photodetector. All in all it sounds like a fairly simple detection problem to me.

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FlatterMann is a new contributor to this site. Take care in asking for clarification, commenting, and answering. Check out our Code of Conduct.
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  • $\begingroup$ Thank you very much. It helps ! I do think the photodiode and our 5W laser works actually it is just that it is difficult to simulate 10 km/s particles and we have been asked to demonstrate by theory/formula and since I am a very beginner in photodetection, I didn’t knew from where I could begin, I tried Mie theory but I didn’t made the results I wanted $\endgroup$
    – Simon M.
    Sep 23 at 23:43

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