Defocusing as a means of light removal from an amplifying medium is studiedβ’ The wave propagation in a simple layer and in an Epstein layer is considered. It is shown that defocusing leads to additional nonsaturatable, nonresonante losses. When defocusing is optimum, it is profitable to operate in the saturation regime with no limitations on the length of the active mediumβ’ Defocusing naturally leads to a single-mode regime and to a high directivity of the output radiationβ’ Experiment showed that defocusing is present in the superluminescence of a dye excited by a narrow knife-shaped pumping beam. The properties of defocusing layers and fibers are, in some respects, familiar to those of unstable resonatorsβ’ PACS: 42.55bi
In optical amplifying elements with a refractive index smaller than that of the environment, there exists defocusing, i.e. a lateral spreading of radiation with respect to the major direction of propagation. In particular, defocusing is observed in plasma layers and filaments which exhibit amplification and are superluminescent radiators [i, 2]. Defocusing can be used to remove light from the active medium and in this capacity it has many attractive features.
Consider the wave propagation in a simple layer and in an Epstein layer [3,4] where the transverse distribution of the dielectric constant e is described, respectively, by