Why can't there be a 2-level laser with Non-Optical Pumping

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Discussion Overview

The discussion revolves around the feasibility of a two-level laser utilizing non-optical pumping mechanisms. Participants explore the principles behind population inversion in lasers and the implications of different pumping methods, including electric current and magnetic fields.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant notes that optical pumping leads to equal probabilities for absorption and stimulated emission, questioning how this principle applies to non-optical pumping.
  • Another participant requests a detailed example of a non-optical pumping mechanism that does not involve light or electromagnetism.
  • A participant mentions that laser diodes achieve population inversion through electric current in a PN junction, suggesting this as a form of non-optical pumping.
  • One participant cites the Ammonia Maser as an example of a two-level laser with non-optical pumping, highlighting its operation in a magnetic field.
  • Another participant clarifies that the Ammonia Maser involves magnetic extraction of excited states but seeks to understand a "local" population inversion without moving atoms.
  • There is a consensus among some participants that if carrier injection in diode lasers is considered non-optical pumping, then two-level non-optically pumped lasers are indeed possible.
  • A later reply questions the origin of the initial inquiry regarding non-optical pumping if diode lasers are valid examples.

Areas of Agreement / Disagreement

Participants express differing views on the applicability of non-optical pumping to two-level lasers. While some agree that diode lasers demonstrate this concept, others seek clarification on the nature of population inversion without physical movement of atoms. The discussion remains unresolved regarding the broader implications of non-optical pumping.

Contextual Notes

Participants express uncertainty about the definitions and mechanisms of non-optical pumping, particularly in relation to population inversion and the dynamics involved. There are unresolved questions regarding the specific criteria that classify a pumping method as non-optical.

Q.B.
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Hi everyone,

I would like to understand the answer to the question in the title.

I got that when we use optical pumping of a laser, the probability, given an incoming photon of adequate energy, for an atom to absorb it and for an other to produce some stimulated emission out of it are equal. Thus the rate equations for the level population cannot be consistent with a stationary population inversion.

However, I couldn't find any justification of why this also applies to non-optical pumping.

I thank you in advance for your answers.
 
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Provide a detailed example of a (hypothetical) non-optical pumping.
ie. Did you have a mechanism in mind that excited electrons but did not involve light/electromagnetism?
 
Thanks for your answer.

For instance, I thought that for laser diodes, the population inversion was realized thanks to some electric current flowing into a PN junction.
 
There definitely are two level lasers with non-optical pumping. Specifically, the Ammonia Maser, which was the first laser constructed (though in the microwave range) operates by separating the exited states from the ground state molecules in a magnetic field.
 
Thanks for your answer. Actually I heard about the maser example, but as you said, it involves a magnetic extraction of the excited state of the two level system. However, I had in mind a "local" population inversion, where one leaves the atoms (excited or not) where they are, but the dynamics of the pumping still creates a population inversion.
 
Q.B. said:
For instance, I thought that for laser diodes, the population inversion was realized thanks to some electric current flowing into a PN junction.
Yup, you are correct. diode laser is a two level (actually, two band) system with pumping by carrier injection. As long as you can get population inversion, you'll get lasing.
 
Q.B. said:
Thanks for your answer.

For instance, I thought that for laser diodes, the population inversion was realized thanks to some electric current flowing into a PN junction.
Great ... so, if that counts as "non-optical pumping", it follows that you can get 2-level non-optically pumped lasers.
Which answers the question in the title.
Well done.

How does the question come up at all in that case?
 

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