Modes and Q-factor(s) of 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?

 

[DaveE]

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]

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.