Why are laser linewidths in frequency domain?

I am learning about the lasers and I find one thing confusing about the lasers.

I understand that there is a range of wavelength laser, it is never exactly monochromatic. So, I understand the concept of FWHM to define a linewidth.

What I have difficulty understanding is this: Why is it often stated in terms of frequency (i.e., kHz, MHz, etc) and not wavelength (in nm)? Is it not more intuitive to work in the wavelength range?

Also, I am confused about some terminology itself. Sources often write "narrow linewidth", but when they also for the opposite, say "high bandwidth". Would it not be better to call it "broad linewidth"?

• Recall frequency times wavelength is $c$. Mar 7 at 2:10
• When a beam travels from one medium to another, the wavelength changes but the frequency stays the same. Mar 7 at 4:19

Thanks to the constant speed of light in a vacuum, we have $$c = \lambda f$$, so there is a direct relation between frequency and wavelength. This allows us to use those values interchangeably. Moreover, the energy of a given photon, which is related to the frequency $$f$$ of the field, not only does not depend on the medium in which light propagates but also depends on it linearly ($$E=h f$$), making that value sometimes more intuitive to use. However, very often, the choice of a specific unit of energy depends on what is common standard among a given community. For example, in the field of spectroscopy, you often see that the energy of photons is presented in units of $$\text{cm}^{-1}$$, i.e., $$1/ \lambda$$.