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

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In summary: It comes up because, in order to stimulate emission from the ground state, you need to pump it up to an excited state. But if the population inversion is already there, then the excited state will stay there and no pumping will be needed.
  • #1
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?
 
  • #3
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.
 
  • #4
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.
 
  • #5
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.
 
  • #6
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.
 
  • #7
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?
 

1. Why is it not possible to create a 2-level laser with Non-Optical Pumping?

The 2-level laser refers to a type of laser system that has only two energy levels, an excited state and a ground state. Non-optical pumping involves using a technique other than light to excite the atoms in the laser medium. However, in order for a 2-level laser to operate, there must be a sufficient population inversion between the two energy levels. Non-optical pumping methods are not able to create this population inversion, making it impossible for a 2-level laser to function.

2. Can other types of pumping be used to create a 2-level laser?

No, the principles of a 2-level laser require the use of optical pumping. This is because the optical pumping process can create a large enough population inversion to achieve laser action. Other types of pumping, such as electrical or chemical, do not have the same ability to create a population inversion and are not suitable for creating a 2-level laser.

3. Are there any benefits to using Non-Optical Pumping in a laser system?

While Non-Optical Pumping cannot be used to create a 2-level laser, it does have its own advantages in certain laser systems. For example, it can be used in solid-state lasers to create a more uniform and stable pumping energy distribution. It is also useful in some gas lasers for creating a high-energy, short-pulse output.

4. What are some common techniques used for Non-Optical Pumping?

Some common techniques for Non-Optical Pumping include electrical pumping, chemical pumping, and inelastic collisions. Electrical pumping involves using an electric current to excite the atoms in the laser medium, while chemical pumping uses a chemical reaction to create the population inversion. Inelastic collisions involve using particles with high kinetic energy to excite the atoms in the laser medium.

5. Are there any ongoing research efforts to overcome the limitations of Non-Optical Pumping in creating a 2-level laser?

Yes, there are ongoing research efforts to find ways to create a 2-level laser using non-optical pumping methods. Some studies have focused on using quantum dots or nanocrystals as the laser medium, which could potentially allow for a population inversion to be created without optical pumping. However, this research is still in its early stages and has not yet resulted in a functional 2-level laser system.

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