# Intracavity Features

Compound cavity lasers have very interesting properties due to the interference between modal combs. The so-called Vernier effect may induce either strongly monomode dynamics or high frequency modal beating, see for instance [8].

This type of dynamics can be studied with Freetwm following a versatile approach: for a low number of intracavity reflectors, one can define several sub-sections, coupled via their respective boundary conditions. However, when the number of intracavity reflector is large, like e.g. to form a rough photonic crystal, this approach is not practical and we provide another method where one can insert directly reflectors inside a single section.

On the left, one can observe the results of this latter approach where harmonic multimode dynamics is induced by placing inside the cavity four 1% intracavity reflectors located at L/2, 5L/8, 3L/4 and 7L/8 within a cavity of length L. In each subsection, one can notice that the population inversion ( D_{0}) evolves around different values due to the compound cavity effect |

The four maxima of the intensity within the cavity indicates that the laser operates in a regime where one mode every eigth is active.