Is it possible to image individual air molecules?

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Discussion Overview

The discussion revolves around the feasibility of imaging individual air molecules, particularly through the use of laser illumination and scattered light to measure molecular motion. Participants explore the theoretical and practical aspects of this concept, including potential applications in microphone technology.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant proposes using laser illumination and Doppler shift measurements to image individual air molecules, suggesting a novel microphone design where air serves as the sensing element.
  • Another participant counters that the scattered light would originate from a large set of molecules, indicating that true imaging of individual molecules is not achievable with this method, although measuring temperature and net motion of rubidium is possible.
  • A participant inquires about calculating the amount of scattered light from air and its dependence on wavelength, indicating interest in practical implementation.
  • Discussion includes the necessity of targeting transition frequencies of gas molecules to effectively measure scattering, with references to existing formulas for absorption in atomic/molecular transitions.
  • One participant mentions the field ion microscope as a related technique capable of imaging individual atoms, although it does not directly address the original question about air molecules.
  • Another participant seeks information on the transition frequencies for air molecules and their spectral range, expressing uncertainty about their location in the electromagnetic spectrum.
  • A later reply suggests that transition frequencies for electronic excitations occur in the infrared and visible to ultraviolet range, providing a partial answer to the inquiry about spectral locations.

Areas of Agreement / Disagreement

Participants express differing views on the possibility of imaging individual air molecules, with some asserting that it is not feasible while others suggest it may be theoretically possible under certain conditions. The discussion remains unresolved regarding the practicality and efficiency of the proposed methods.

Contextual Notes

Limitations include the dependence on specific transition frequencies and the efficiency of detecting small effects in the proposed microphone design. There are unresolved questions about the spectral characteristics of air molecules.

Hunter235711
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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.
 
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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.
 
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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).
 
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.
Hunter235711 said:
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.
 
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.
 
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mfb said:
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.
 

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