# Modes and Q-factor(s) of a random laser

• samchan
In summary, the conversation discusses the Q-factor of random lasers and how it is calculated. It is mentioned that random lasers have multiple peaks close to each other and the question is raised whether each peak corresponds to a unique random lasing mode. It is also mentioned that the Q-factor may not be well defined for complex oscillators and a more detailed model may be needed to explain it. Additionally, a paper is referenced where the Q-factor is calculated for isolated peaks in a random laser.
samchan
Many papers about random lasers mention the Q-factor of random lasers. Since a random laser has multiple peaks close to each other like shown in the figure. Does each of these peaks correspond to a unique random lasing mode, or is it just a single mode?

Similarly what is the right way to calculate the Q-factor of this random laser (example plot shown below) : Should it be wavelength at Peak1 divided by FWHM at (blue line) or wavelength of Peak1 divided by FWHM at (red line) ?

Should the Q-factor be calculated at -3db or FWHM?

IMO, Q is only well defined for simple oscillators. I'm not sure that there is a way to describe two response peaks with one value. You will probably have to explain to people what is going on with more words or a more detailed model. Perhaps as the sum of two peaks each with their own λ and Q?

samchan
DaveE said:
IMO, Q is only well defined for simple oscillators. I'm not sure that there is a way to describe two response peaks with one value. You will probably have to explain to people what is going on with more words or a more detailed model. Perhaps as the sum of two peaks each with their own λ and Q?

I saw another paper, where they calculate Q-factor for isolated peaks in a random laser. Below is a picture from a paper titled : Random Lasing with a High Quality Factor over the Whole Visible Range Based on Cascade Energy Transfer. They measure bandwidth of 0.05nm at FWHM.

## What is a random laser?

A random laser is a type of laser that uses a disordered or random medium instead of a traditional cavity to amplify light. This results in a broad emission spectrum and multiple lasing modes.

## What are the modes of a random laser?

The modes of a random laser refer to the different wavelengths of light that are amplified and emitted by the laser. These modes are not fixed and can vary depending on the properties of the random medium.

## What is the Q-factor of a random laser?

The Q-factor of a random laser is a measure of its quality or efficiency. It is calculated by dividing the energy stored in the laser's cavity by the energy lost per cycle. A higher Q-factor indicates a more efficient laser.

## How is the Q-factor of a random laser affected by its modes?

The Q-factor of a random laser is affected by its modes because each mode has a different energy loss rate. As the number of modes increases, the Q-factor decreases due to the increased energy loss.

## What are the applications of random lasers?

Random lasers have potential applications in imaging, sensing, and telecommunications. They can also be used as light sources in displays and in medical and industrial applications. Research is ongoing to explore their potential in these areas.

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