Topic summary
Laser cavity
Extracted from the Wikipedia article Optical cavity.
Practical resonators
If the optical cavity is not empty (e.g., a laser cavity which contains the gain medium), the value of L needs to be adjusted to account for the index of refraction of the medium. Optical elements such as lenses placed in the cavity alter the stability and mode size. In addition, for most gain media, thermal and other inhomogeneities create a variable lensing effect in the medium, which must be considered in the design of the laser resonator.