Disordered systems that both scatter and amplify light (the so-called random lasers) have been a fascinating subject to study. Over the last five years, there have been substantial theoretical and experimental efforts to unravel the mechanism that gives rise to this amazing behavior.
A model to simulate the phenomenon of random lasing is presented. It couples Maxwell’s equations with the rate equations of electronic population in a disordered system. Finite difference time domain methods are used to obtain the field pattern and the spectra of localized lasing modes inside the system. A critical pumping rate exists for the appearance of the lasing peaks. The dependence of on the length of the system and the strength of disorders is obtained. The number of lasing modes increases with the pumping rate and the length of the system. There is a lasing mode repulsion. This property leads to a saturation of the number of modes for a given size system and a relation between the localization length and average mode length . Similar behavior is expected to be seen in photonic crystals, too.