Overview

From a physical point of view, the principal difference between large and small intermode frequency spacings is determined by their relation to the frequency of dynamical processes in lasers.

In Chapter 4 we have discussed models, in which

The intermode beat frequencies suggested frequencies that are much greater than relaxation oscillation frequencies in the class B lasers and are situated essentially higher than all the frequencies characteristic for the spectral dynamics of dye lasers. Therefore, we did not take into account the mode beats in the considered rate equation models. Combination tone mode-mode couplings, which occur via oscillating inversion gratings, also do not require the presence of amplitudes of these gratings among the variables.

Such an approach is incorrect if the modes are close in frequencies. In this case the amplitudes of oscillating inversion gratings are included in the variable collection, making the system's dimension higher and changing its physical properties.

In contrast to the simple rate equation models, an important role is played not only by the amplitudes but also by phases of the physical quantities that characterize the state of the field and the medium. That is way we use the term 'model with the phase-sensitive interaction'.

The phase-sensitive interaction takes place between a pair of levels and it is reasonable to study this phenomenon considering the two-mode models. It is important to indicate the type of the resonator. In Fabry-Perot cavities the modes are standing waves and the phase-sensitive interaction occurs here in addition to...