# Laser action and stimulated emission

• logearav
In summary, when an electron in ground state absorbs a photon of energy equivalent to the energy difference between its ground and excited state, it transitions to an excited state. After a period of time, it returns to the ground state by emitting a photon, a process known as spontaneous decay. In order to achieve laser action, population inversion and stimulated emission must occur. This can be achieved by supplying a photon to the electron in the metastable state, E2, which triggers stimulated emission. The energy of the supplied photon is E2 - E1.
logearav

## Homework Statement

Revered Members,
An electron in ground state makes its way to an excited state upon absorption of photon of energy, equivalent to energy difference between ground state and excited state, and after some time, it decays by emitting the photon and returns to the ground state. This is called spontaneous decay.
For Laser action, population inversion and stimulated emission should occur.

## The Attempt at a Solution

Now let me explain the scenario
1) An atom(electron) in the energy level E1 absorbs a photon and goes to a state of higher energy say E3
2) While decaying from E3 to E1, it reaches a metastable state E2. Now, due to longevity of the stay in E2 than in E3, we can achieve population inversion in E2
My question is ,
1) Do we supply a photon to the electron which stays in the meta stable state E2, so as to trigger stimulated emission?
2) If yes, what is the energy of the supplied photon. Is it E3 - E1 or E2 - E1?

logearav said:
My question is ,
1) Do we supply a photon to the electron which stays in the meta stable state E2, so as to trigger stimulated emission?
Yes[/quote]2) If yes, what is the energy of the supplied photon. Is it E3 - E1 or E2 - E1?[/quote]
http://en.wikipedia.org/wiki/Stimulated_emission
E2-E1

The rest is just how you go about populating E2.

Thanks for the reply Simon. So I infer that the electron in the metastable state has already has an absorbed photon, and if we supply a photon of energy E2 - E1 externally, then this photon plus the absorbed photon are emitted and both are in same phase. Am I right?

Last edited:
The electron in energy level E2 does not "have an absorbed photon"; it simply has energy. In fact it has an amount of energy E2-E1 more than it would have if it were in the ground state. When the electron makes a transition to level E1, that energy is converted to electromagnetic energy, i.e., the emitted photon.

Hope that helps.

+1 to Redbelly98:

It's not a useful picture to think of the electron as somehow holding-on-to a photon that gets released later.

The electron has absorbed a photon to get it to E3 already - that photon has been destroyed and it's energy converted electromagnetic potential energy for the electron.
When the electron decays to E2 it has to release some of that energy ... there are several ways it can do this but the most likely one by far is to release a single photon to carry off the energy difference.

Thank you Redbelly and Simon. So, when the electron releases photon when it comes to E2, we supply again a photon of energy E2 - E1 and the supplied photon acts as stimulating photon. Am I right?

Yes.

## 1. What is laser action?

Laser action refers to the production of a highly concentrated and coherent beam of light through a process called stimulated emission. This happens when a photon of a specific wavelength interacts with an excited atom, causing it to release two photons that are in phase and travel in the same direction.

## 2. What is stimulated emission?

Stimulated emission is a process in which an excited atom or molecule emits a photon of light when it interacts with another photon of the same frequency. This results in the amplification of light and the production of a laser beam.

## 3. How does stimulated emission differ from spontaneous emission?

Spontaneous emission occurs when an excited atom or molecule releases a photon of light without any external interaction. In contrast, stimulated emission requires the presence of an external photon to trigger the emission of a second photon, resulting in a more intense and coherent output of light.

## 4. What is the difference between a laser and a regular light source?

A laser produces a highly focused, monochromatic, and coherent beam of light, while a regular light source emits light in all directions and at different wavelengths. Laser light is also much more intense and has a narrower beam compared to regular light sources.

## 5. What are some common applications of laser technology?

Laser technology has a wide range of applications in various fields such as medicine, communications, manufacturing, and scientific research. Some common uses include laser surgery, barcode scanners, laser printers, cutting and welding metals, and measuring distances and speeds in scientific experiments.

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