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physica status solidi (b)

Exciton Nonequilibrium Steady States in Laser‐Excited Molecular Crystals

Nguyen Ba An

Published Dec 1, 1988• 9 citations
Publisher

Abstract

Abstract Nonequilibrium steady states of excitons in laser‐excited three‐dimensional molecular crystals are investigated not resorting to the usual boson description but using the exact trilinear commutation relations for exciton operators. The nonequilibrium property, non‐bosonity, and optical nonlinearity of the many‐exciton system under the action of an external classical laser field are considered on the same footing. Eigenfrequencies and dampings of the giant polariton are found to be dependent on the excitation degree. Conditions are determined for two types of bistability: density–light and light–light bistability.

DOI
10.1002/pssb.2221500277

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Abstract Nonequilibrium steady states of excitons in laser‐excited three‐dimensional molecular crystals are investigated not resorting to the usual boson description but using the exact trilinear commutation relations for exciton operators. The nonequilibrium property, non‐bosonity, and optical nonlinearity of the many‐exciton system under the action of an external classical laser field are considered on the same footing. Eigenfrequencies and dampings of the giant polariton are found to be dependent on the excitation degree. Conditions are determined for two types of bistability: density–light and light–light bistability.
The present article shortly reviews some recent results in the study of excitonic nonlinearity in optically excited media using a nonboson treatment for many-exciton systems. After a brief discussion of the exciton nonbosonity the closed commutation relations are given for exciton operators which hold for any exciton density and type. The nonboson treatment is then applied to the problems of intrinsic optical bistability and nonlinear polariton yielding quite interesting and new effects, e.g. new shapes of hysteresis loops of intrinsic optical bistability or anomalies of polariton dispersion.
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We analyze elementary properties of exciton and polariton lasers --- devices that generate coherent optical and matter waves using final-state stimulation of exciton-phonon scattering. First we discuss the relation between the conditions for the onset of equilibrium and nonequilibrium excitonic condensates. Provided that the thermal de Broglie wavelength ${\ensuremath{\lambda}}_{\mathit{T}}$ exceeds the exciton Bohr radius aB{\mathit{a}}_{\mathit{B}}aB​, an exciton laser operates without electronic population inversion. In contrast to previous proposals, this is a different type of laser without inversion which utilizes many-body coherences. When the excitonic character of the polariton branch vanishes, a polariton laser becomes indistinguishable from a photon laser. \textcopyright{} 1996 The American Physical Society.
Abstract A joint effect of exciton–phonon and exciton–exciton interactions on optical properties of semiconductors is studied. In these substances the exciton density is shown to be a multivalued function of incident light intensity and the frequency and temperature conditions under which the optical bistability arises are specified. Investigation of nonlinear optical properties of semiconductors with account for the indirect phototransitions exhibits that both multistable optical states and the bistable ones distinguished by a complicated dynamics of the switching may be observed in such systems.
The study of time development is indispensable for a system of excitons and bi-excitons at high density because this exists only as a transient state. Here we study theoretically the population dynamics of excitons and bi·excitons both under the. pulse and steady excitations where photons and phonons emitted in the chemical processes of this system can be considered as the irrelevant external system. Under the opposite condition where the radiation field composes the relevant system, the laser action due to the radiative decay of bi ·excitons is discussed.