Number of Photons inside a Laser Cavity

In summary, the conversation discusses determining the number of photons present in a laser cavity with two mirrors of different reflectivities. The person is having trouble understanding how to calculate this with the given information. They suggest working backwards from the output mirror's reflectivity, but are unsure of the significance of N(out). Ultimately, they are asked to post this question in a different forum for help with their homework.
  • #1
HuskyLab
8
0
<< Mentor Note -- thread moved from the technical forums, so no Homework Help Template is shown >>

Let's say you have a laser cavity with two mirrors at either end, one is considered 100% reflective, the other 99.9%, so that a wave beam is emitted through this lower reflectivity mirror.
I know:
-The length of the laser cavity
-The reflectivity of the mirrors
-The power and wavelength of the emitted wave beam

I am asked to determine the number of photons present in the cavity (I presume average considering they are continually being absorbed and re-emitted). I am having a hard time understanding how to even go about this with the, at least what seems to me, limited information.

I thought about working backwards, if let's say the output mirror has a reflectivity of 99.9%, then only 0.1% of the photons inside have been emitted so N(out)/0.001 would give the average number of photons inside the cavity? I feel like I'm missing something. I know that the photons interfere to create standing waves some integer multiple fitting the cavity length.
 
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  • #2
HuskyLab said:
I am asked...
Asked by whom?
 
  • #3
Nugatory said:
Asked by whom?
By my teacher.
 
  • #4
HuskyLab said:
By my teacher.
In that case, we're going to have to ask you to post this question to the "Introductory Physics Homework" subforum instead.

[Edit: looks like Berkeman beat me to it]
 
  • #5
HuskyLab said:
I thought about working backwards, if let's say the output mirror has a reflectivity of 99.9%, then only 0.1% of the photons inside have been emitted so N(out)/0.001 would give the average number of photons inside the cavity?
N(out) is what, exactly?
 
  • #6
When the cavity reaches a state of equilibrium, what could you say about it?
 

FAQ: Number of Photons inside a Laser Cavity

1. How is the number of photons inside a laser cavity determined?

The number of photons inside a laser cavity is determined by the population inversion of the atoms or molecules in the laser medium. This is a measure of the excess of atoms or molecules in the excited state compared to the ground state. The higher the population inversion, the more photons are present in the cavity.

2. What factors affect the number of photons inside a laser cavity?

Several factors can affect the number of photons inside a laser cavity. These include the type and concentration of the laser medium, the pumping rate, the cavity size and shape, and the reflectivity of the cavity mirrors. Temperature and external environmental factors can also play a role.

3. How does the number of photons inside a laser cavity relate to the laser's output power?

The number of photons inside a laser cavity is directly proportional to the laser's output power. This means that as the number of photons increases, so does the laser's output power. However, other factors such as the laser's efficiency and the quality of the cavity mirrors also play a role in determining the output power.

4. Can the number of photons inside a laser cavity be controlled?

Yes, the number of photons inside a laser cavity can be controlled by adjusting the pumping rate, the laser medium, and the cavity parameters. By carefully controlling these factors, the number of photons can be optimized for a desired output power and laser performance.

5. How does the number of photons inside a laser cavity affect the laser's performance?

The number of photons inside a laser cavity is a crucial factor in determining the laser's performance. A higher number of photons can lead to a higher output power and better beam quality. It also affects the laser's threshold and efficiency, as well as its ability to maintain a stable output. Therefore, it is important to carefully control and monitor the number of photons inside a laser cavity for optimal performance.

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