EV per Torr*cm -- What does it mean?

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Discussion Overview

The discussion revolves around the meaning of the unit "eV per Torr*cm" as mentioned in the context of nitrogen lasers. Participants explore its implications in terms of ionization energy and the relationship between pressure and energy in gas discharges.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about the meaning of "80 to 100 eV per Torr*cm" and questions whether it refers to energy in a specific volume at a given pressure.
  • Another participant explains that the unit represents an ionization constant related to Paschen's Law, linking electric field strength to energy per collision required for ionization.
  • This explanation includes the assertion that the pressure affects the mean free path length, which in turn influences the energy per collision.
  • A later reply reiterates the explanation of the unit as an ionization constant and emphasizes its relevance to achieving the energy necessary to excite the lasing state.
  • One participant provides a mathematical breakdown of the unit in SI terms, detailing the conversion from eV per Torr*cm to other units, though this is not universally acknowledged or verified by others.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on the interpretation of the unit, with some clarifications provided but also expressions of confusion and differing perspectives on its implications.

Contextual Notes

The discussion includes varying interpretations of the unit and its application, with some participants providing mathematical insights while others focus on conceptual understanding. There is no resolution on the initial confusion expressed.

DariusP
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I was reading about this
https://en.wikipedia.org/wiki/Nitrogen_laser

and it says "80 to 100 eV per Torr*cm pressure of nitrogen gas". I'm finding this a little bit confusing. It needs some specific amount of energy in a centimeter of volume with 1 Torr of pressure?
 
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I don’t see that in the article, but I can explain the unit.

That is an ionization constant. See the wiki article on Paschen’s Law:
https://en.m.wikipedia.org/wiki/Paschen's_law
This constant relates the electric field strength to the energy per collision required to cause ionization and so sustain a discharge. The pressure is in there because the energy accumulated by a particle depends on the distance over which it is accelerated by the field, so the energy per collision depends on the mean free path length which is inversely proportional to the pressure.

Note that for a laser this constant is not necessarily for the minimum energy for discharge, but sets the energy per collision high enough to excite the lasing state.
 
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Cutter Ketch said:
I don’t see that in the article, but I can explain the unit.

That is an ionization constant. See the wiki article on Paschen’s Law:
https://en.m.wikipedia.org/wiki/Paschen's_law
This constant relates the electric field strength to the energy per collision required to cause ionization and so sustain a discharge. The pressure is in there because the energy accumulated by a particle depends on the distance over which it is accelerated by the field, so the energy per collision depends on the mean free path length which is inversely proportional to the pressure.

Note that for a laser this constant is not necessarily for the minimum energy for discharge, but sets the energy per collision high enough to excite the lasing state.
Love you, thank you very much
 
it is in surface area units. In SI units it is
eV per Torr*cm=##\frac{q_e*V}{Torr*cm}=\frac{1.60217646*10^{-19}*C*V}{133.322*Pa*m/100}=\frac{1.60217646*10^{-17}*C*V}{133.322*N/m}=1.2017344924318567*10^{-19}*m^2##
 

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