Laser Broadening: Impact on Wavelengths

[chrisphd]

In Quantum mechanics lectures we are learning that several factors influence the wavelength produced from a laser. These factors include doppler broadening of moving atoms in the laser, the uncertainty of the transition energy levels themselves due to the uncertainty principle, etc. Previously we learned that in a laser cavity of length L, due to boundary conditions, only certain wavelengths are possible, ie, wavelength*n/2 = L, where n is an integer.

Question:
Shouldn't the boundary condition limit the output of a laser to a single frequency rather than a small range of frequencies from w to w+dw?

 

[f95toli]

No, because there is no such thing as a cavity with an exact length.
Fabry-Pérot etalons (which are essentially "cavities") can be used to stabilize lasers, but they are still be limited by variations in the length due to e.g. thermal variations.
Building good etalons is almost a field of its own in science (I know a couple of people who spend ALL their time doing it) and you should be able to find plenty of papers that describes how it is done.