Abstract. Scattering of resonant radiation in a dense two-level medium is studied theoretically with account for local field effects and renormalization of the resonance frequency. Intrinsic optical bistability is viewed as switching between different spectral patterns of fluorescent light controlled by the incident field strength. Response spectra are calculated analytically for the entire hysteresis loop of atomic excitation. The equations to describe the non-linear interaction of an atomic ensemble with light are derived from the Bogolubov-Born-Green-Kirkwood-Yvon hierarchy for reduced single particle density matrices of atoms and quantized field modes and their correlation operators. The spectral power of scattered light with separated coherent and incoherent constituents is obtained straightforwardly within the hierarchy. The formula obtained for emission spectra can be used to distinguish between possible mechanisms suggested to produce intrinsic bistability in experiments.
We consider a model of atomic radiators in a dielectric medium and its optical characteristics. In the framework of the microscopic approach and the Bogolyubov-Born-Green-Kirkwood-Yvon method, we obtain a chain of coupled equations for reduced density matrices and correlation operators of atomic particles and modes of a quantized field. We derive a closed system of equations describing the evolution of radiators in the model medium under the action of external radiation. We calculate the effective spontaneous relaxation rate in the presence of the local field produced by the medium. For the first time, we demonstrate the relation between micro and macro approaches to the solution of the problem involving a change in the spontaneous radiation rate in the medium.
The correlation between the photoluminescence intensity of a dye-sensitizer (methyl pheophorbide-a, MPP-a) and the efficiency of the singlet oxygen ( 1 𝑂2) generation is studied. The excitation spectrum of 1 𝑂2 emission at 1270 nm has one strong band at 403 nm that coincides with the Soret band of MPP-a and only a weak peak at 667 nm, which practically coincides with the strongest band of the MPP-a excitation spectrum. Therefore, the choice of an excitation wavelength for the efficient 1 𝑂2 generation should be based on direct measurements of the excitation spectra of the sensitized 1 𝑂2 emission. K e y w o r d s: singlet oxygen, photodynamic therapy, photosensitization, dye sensitizer, methyl pheophorbide-a.
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