I Is it possible to image individual air molecules?

[Hunter235711]

I was wondering if it is possible to image the motion of individual air molecules? What I am picturing is using a laser to illuminate a volume of air, and using scattered light to measure the velocity of individual air molecules through the doppler shift of the scattered light. It seems that this would allow sound waves passing through the air to be detected.

In essence it seems you could build a microphone where the air itself if the sensing element.

 

[mfb]

What you describe is not imaging individual air molecules, as your scattered signal comes from a large set of molecules. It is possible to measure the temperature and the net motion of rubidium that way, air is more challenging as the required photon energy is higher, but I guess in principle it is possible as well.

 

[Hunter235711]

Ah, that makes sense. So, say I want to actually go about building such a microphone. How could I calculate the amount of scattered light from an illuminated volume of air? Also, how does this depend on wavelength?

If such a microphone could be constructed it would have the benefit that there is no impedance discontinuity between the air and the sensing medium (also air).

 

[mfb]

You would have to hit one of the transition frequencies of atoms/molecules in the gas, and then scan over the frequency range of the spectral line. There are formulas for the absorption of electromagnetic radiation in atomic/molecular transitions.

If such a microphone could be constructed it would have the benefit that there is no impedance discontinuity between the air and the sensing medium (also air).

Yes, but it would be horribly inefficient because it would look for a tiny effect.

 

[pixel]

Not what you asked about, but related (from Wikipedia article on the Field Ion Microscope):

The field ion microscope is a type of microscope that can be used to image the arrangement of atoms at the surface of a sharp metal tip. It was the first technique by which individual atoms could be spatially resolved.

 

[Hunter235711]

You would have to hit one of the transition frequencies of atoms/molecules in the gas

How can I find more information about where these transition frequencies would occur for air? I don't even know if they would be in the microwave/infrared/visible part of the spectrum.

 

[mfb]

Infrared and visible to ultraviolet for electronic excitations.
Google finds various websites