Abstract
The work based on a semiclassical description, presents the results of studying the processes of absorption and radiation of a field in the form of a standing wave in a waveguide filled with a two-level active medium. Under conditions of spatial inhomogeneity of the field intensity, interference of quasi-periodic oscillations of population inversion occurs in different local regions of the waveguide. A quasiperiodic change in population inversion is determined by the Rabi frequency, which is known to be associated with the probability of induced radiation with a positive population inversion, or induced absorption with its negative value. Since the population inversion change is accompanied by absorption or emission of field quanta, this leads to the exchange of energy between the field and the active medium located in the waveguide. It is shown that the attenuation of a large-amplitude field to a waveguide filled with an unexcited active medium is nonlinear. In the developed mode, this process has the character of energy exchange between the field and the active medium. In this case, the wave attenuation is replaced by its growth, just as it happens in the well-known case of Landau kinetic damping. Competition of the processes of radiation and absorption leads to the fact that the nature of the oscillations (nutations) of the population inversion at different points of the waveguide space is different. The interference of nonsynchronous spatially localized oscillations of the population inversion in the volume of the waveguide leads to changes in the field amplitude. The paper also discusses the process of field excitation in a waveguide with a pre-inverted two-level active medium, taking into account external mechanisms for the absorption of wave energy. Consideration of these problems is important for understanding the processes of generation of induced radiation, which, as noted by C. Towns, is to a large extent coherent radiation.
Highlights
The work based on a semiclassical description, presents the results of studying the processes of absorption and radiation of a field in the form of a standing wave in a waveguide filled with a two-level active medium
A quasiperiodic change in population inversion is determined by the Rabi frequency, which is known to be associated with the probability of induced radiation with a positive population inversion, or induced absorption with its negative value
We show that the interference of quasi-periodic changes in population inversion in different areas with the Rabi frequency, depending on the local field intensity in these areas, determines both the nature of the attenuation of a large amplitude wave and the nature of the field generation
Summary
The work based on a semiclassical description, presents the results of studying the processes of absorption and radiation of a field in the form of a standing wave in a waveguide filled with a two-level active medium. A consequence of the limitations of the system is the appearance of line spectra of oscillations and standing waves, which leads to a noticeable non-uniformity of the field intensity distribution This can change the nature of the field interaction with the active medium placed in the waveguide, because in areas with different field intensities the Rabi frequency and, the nature of the oscillatory behavior of the population inversion of the active substance will differ significantly. We show that the interference of quasi-periodic changes in population inversion in different areas with the Rabi frequency, depending on the local field intensity in these areas, determines both the nature of the attenuation of a large amplitude wave and the nature of the field generation. The aim of the article is to present the physical mechanism of attenuation of a large-amplitude wave in a waveguide filled with an active two-level medium, as well as to elucidate the nature of electromagnetic field excitation at finite levels of population inversion
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