The biexciton optical Stark-effect under resonant pumping between the exciton and biexciton levels is studied theoretically. The probabilities of biexciton two-photon absorption of a weak probe light and of one-photon biexciton-exciton transition are calculated. The optical Stark splitting manifests itself in two-photon biexciton absorption through two absorption peaks spaced 2 (Omega) apart. Omega is the Raby frequency. In the luminescence spectrum due to biexciton-exciton one-photon transition three luminescence maxima appear which are shifted with respect to the luminescence maximum in the case without pumping.
The biexciton optical Stark-effect under resonant pumping between the exciton and biexciton levels is studied theoretically. The probabilities of biexciton two-photon absorption of a weak probe light and of one-photon biexciton-exciton transition are calculated. The optical Stark splitting manifests itself in two-photon biexciton absorption through two absorption peaks spaced 2 (Omega) apart. Omega is the Raby frequency. In the luminescence spectrum due to biexciton-exciton one-photon transition three luminescence maxima appear which are shifted with respect to the luminescence maximum in the case without pumping.
Abstract In this paper, we examine the three-level optical Stark effect of excitons in InGaAs/InAlAs quantum dots using renormalized wavefunction formulation. The system was assumed to be irradiated by two lasers in which a strong laser dynamically couples electron-quantized levels, while a weaker laser probes interband absorption. Our results show that, in the presence of the resonant strong laser, two new absorption peaks of excitons appear in the absorption spectrum as a clear indication of the effect. In addition, we propose that the formation of the effect in low-dimensional structures could have connection to the splitting of electron levels. Furthermore, we seek to explain the essential dependence of the amplitude and position of two peaks on pump field detuning.
The theory of the optical Stark effect is developed for quantum-size structures. The effect is due to the interaction of the electron system with intense light, whose frequency, (omega) , is in resonance between two subbands in the conduction band. The probe light of the frequency (Omega) falls in resonance with the adjacent transition between the ground state and the state with an electron-hole pair. In the quasi-steady-state mode, the singularities in the interband (Omega) -light absorption spectra are related to the critical points of the bands, rearranged by the (omega) - light. The shape of the higher conduction band can be evaluated from the spectral positions of the singularities. In the case of two-photon interband transitions, a sharp dependence of the absorption on the light intensity is predicted. In the non-steady-state mode, the probe beam consists of two femtosecond (Omega) -light pulses following each other with the delay time, (tau) d. The dependence of energy, absorbed from the second pulse, on the (tau) d value is calculated. Under the (omega) -pumping, one of the two phenomena should be observed, depending on the type of band structure, namely, the decay of the induced polarization with the characteristic time approximately 1/(omega) R or oscillations with the frequency approximately (omega) R, where (omega) R is the Rabi frequency. The principal effect, controlling the decay of the Rabi oscillations, is the spreading of the packet of states generated by the (Omega) -light pulse.
We show that a laser beam, tuned in the transparency region of a direct-gap semiconductor, not only shifts but also splits the exciton levels. This splitting originates from the degeneracy of the valence band as the (${\ensuremath{\sigma}}_{+},{\ensuremath{\sigma}}_{\ensuremath{-}}$) parts of the light are not similarly coupled to the various exciton components. In the case of a fourfold-degenerate valence band, we find that, at large detuning, the shifts of the (2\ifmmode\times\else\texttimes\fi{}4) eightfold exciton are exactly the shifts of a (2+4) six-level atom. This is just the generalization of the simple band-structure case with one electron and one hole band in which the large detuning excitonic shift has the same value as that of the two-level (dressed) atom. We give the selection rules to observe the various shifted lines for typical pump-probe experiments. We also discuss the experimental conditions necessary to see an exciton red shift at the two-photon absorption threshold, when the molecular biexciton is stable.
Abstract The nonlinear optical phenomena associated with the formation of virtual biexcitons in direct gap semiconductors are studied. Relations are set up for real‐space two‐fermion operators using methods similar to those used when deriving a well known conservation law of k‐space operators for intraband and interband transitions. Restricting the analysis to the χ(3) level, or set of density matrix equations are obtained for the exciton‐biexciton system. Analytical solutions in the limit of small detuning show that the biexcitonic induced absorption and the dynamical Stark effect are closely related, and that the Stark shift as function of the pump frequency has a pole at the frequency of the exciton‐to‐biexciton transition.
Large, nonlinear-optical phenomena are shown theoretically to be observable under nearly two-photon resonant pumping of the excitonic molecule (EM), e.g., in a CuCl crystal. When the exciton polariton (EP) is resonantly pumped into the EM, they are hybridized with each other and show optical Stark splitting. These splittings can be observed, respectively, as a sharp dip in the reflection spectrum and two-photon absorption spectrum due to the EM. We can also clarify how these splittings change into the blueshifts and redshifts of the EP and the EM as functions of the pump frequency and power. The generation of the phase-conjugated wave is shown also to be enhanced under two-photon resonant pumping of the EM. Some characteristics about pump-probe frequency and polarization dependences are also clarified. We have also derived the effective Hamiltonian of the exciton and the EM from the first-principles equation of motion for the exciton coupled with that of the EM. This Hamiltonian has made possible the theoretical analysis of these nonlinear-optical phenomena.
We have studied two-photon nonlinear optical effects arising in a microcavity geometry from resonant two-photon absorption or second-harmonic generation. The transmission spectrum of the cavity is shown to depend on light intensity according to a simple two-level picture with an intensity-dependent coupling: at resonance the system exhibits a two-photon Rabi splitting. The absorption spectrum of a weak probe beam in a pumped cavity is found to strongly depend on pump intensity and detuning; the resulting effect is a sort of two-photon analogue of the usual optical Stark effect. For moderate pump intensities a two-level picture with a pump-dependent coupling can account for the main results, while at higher intensities new unexpected features show up; in particular, we predict the appearance of gain in well-determined spectral regions due to hyper-Raman processes. Finally, we have shown how the coupling coefficients appearing in our formalism can be obtained from a detailed knowledge of the material and geometrical properties of a specific system. For illustrative purposes, we have estimated the required light intensities using realistic data for a GaAs-based semiconductor microcavity.