Transmission Spectra of a Layer of Active Atoms upon Inhomogeneous Broadening

Abstract

Estimation of conditions for manifestation of bistability in the resonance curves of the transmission of a layer of active atoms with inhomogeneous broadening has been made. It is shown that hysteresis in the frequency dependence of such a layer is possible only under the conditions of the Stark shift of the resonant transition levels.Keywords: frequency optical bistability, self-modulation broadening of a spectral line. Introduction.Investigation of the processes of formation of a resonant circuit of absorption of a layer of active atoms may be of interest for elucidating the conditions for observing bistable transmission properties [1][2][3][4]. The bistability or hysteresis property in optical systems excited by laser radiation is easily exhibited upon change in the excitation amplitude [5]. The study of the conditions of the frequency bistability of optical systems, including planar structures of reduced dimensionality, is worth applying when creating up-to-date devices for transmission, storing, and processing of information.Formulation of the Problem and Description of the Approach. We have carried out calculation of resonance curves of a nonlinear-absorption medium, which is represented by an ensemble of active atoms. The main task is to determine the role of the inhomogeneous broadening (of the Gaussian-form spread in the basic frequencies ω 0 of active particles about the line center Ω) in formation of the spectral dependence of absorption at a high level of saturation. Here, allowance for the Stark shift of the levels of the basic transition in an intense light field is also a matter of principle.We considered the case where a monochromatic signal was incident on an active-medium layer filling a cavity. The external signal corresponds to a plane light wave with carrier frequency ω and amplitude E i (t), which is normal to the layer surface and which relatively slowly changes in a time comparable with the period 2π/ω. Interaction of the light wave with the medium of the layer can be described on the basis of the semiclassical approach represented by the Maxwell-Bloch model that enables one to investigate the dynamic behavior of resonant systems under the conditions of exposure to optical fields. Such a system of the equations in the form presented in [3] is used to formulate the relationship given below. In this work, the expression for the polarization response of the medium is modified, first, with allowance for the generalized two-level scheme (similarly, for example, to [6]). Its use permits one to consider, in a certain approximation [7], the role of the self-modulation line broadening due to the Stark effect. Second, inhomogeneous broadening was taken into account in a traditional form, wherein single atoms are characterized by homogeneously broadened lines, which are narrower than the total spectral lines of the whole collection of atoms. Such narrow lines, each corresponding to an individual group of atoms with the same transition frequency ω 0 , are called the spin packets. The expression used f...