Abstract The non‐linear optical nutation on the transitions between IS and 2P exciton states of the Cu2O yellow series is considered theoretically taking into account their degeneracy and polarization properties. The problem is solved under various initial conditions for certain definite orientations of the electrical component of the laser field that causes the interexciton transitions. It is shown that the exciton and photon concentrations vary periodically in time within a certain range near their steady equilibrium values which coincide with the stationary ones. The nutation frequencies are found. A stationary condition is obtained and the stationary frequencies and concentrations are determined.
Abstract The non‐linear optical nutation on the transitions between IS and 2P exciton states of the Cu2O yellow series is considered theoretically taking into account their degeneracy and polarization properties. The problem is solved under various initial conditions for certain definite orientations of the electrical component of the laser field that causes the interexciton transitions. It is shown that the exciton and photon concentrations vary periodically in time within a certain range near their steady equilibrium values which coincide with the stationary ones. The nutation frequencies are found. A stationary condition is obtained and the stationary frequencies and concentrations are determined.
Abstract The nonlinear nutation on the optical transitions between the IS(Λ ) and 2P(Λ , 2Λ , Λ , Λ ) exciton states of the Cu2O yellow series is studied theoretically. An idealized case is considered when one coherent excitonic mode of a macroscopic amplitude is created in the 2P(Λ ) state by the external resonant pumping. It is shown that in this case the CO2‐laser induced dipole transition scheme is the same as for the model equidistant three‐level system. The evolution of the nonstationary state of the exciton–photon system to the stationary one due to the polarization damping is considered. The phase diagrams are investigated both, at strong and weak damping.
Optical nutation in the exciton range of spectrum is studied in the mean field approximation taking into account exciton-photon and elastic exciton-exciton interactions. It is shown that the features of nutation development are determined by the initial exciton and photon densities, the resonance detuning, the nonlinearity parameter, and the initial phase difference. For nonzero initial exciton and photon concentrations, three regimes of temporal evolution of excitons and photons exist: periodic conversion of excitons to photons and vice versa, aperiodic conversion of photons to excitons, and the rest regime. In the rest regime, the initial exciton and photon densities are nonzero and do not change with time. The oscillation amplitudes and periods of particle densities determined by the system parameters are found. The exciton self-trapping and photon trapping appearing in the system at threshold values of the nonlinearity parameter were predicted. As this parameter increases, the oscillation amplitudes of the exciton and photon densities sharply change at the critical value of the nonlinearity parameter. These two phenomena are shown to be caused by the elastic exciton-exciton interaction, resulting in the dynamic concentration shift of the exciton level.
Abstract The quasiequilibrium state of the two‐component non‐linear ortho‐para‐exciton gas is investigated. The concentration shifts of the exciton levels are taken into account at high densities of quasiparticles. Three exciton phases appear at any value of the chemical potential, due to the effect of optical bistability: the para‐phase, the ortho‐phase and the mixed ortho‐para‐phase. It is pointed out that Bose‐Einstein condensation (BEC) in the para‐ and ortho‐phase is possible, in spite of the fact that the initial level of ortho‐excitons is situated higher on the energetic scale than the initial level of para‐excitons.
A theoretical study is carried out of quantum beats (QB) in the time-dependent intensities of absorption of a test pulse and of spontaneous luminescence in a Cu2O crystal under conditions of double optical resonance. It is assumed that pumping is effected by a CO2-laser pulse which dynamically couples the exciton levels 1s(Γ 5 + ) and 2p(Γ 4 − ,Γ 5 − ,Γ 3 − Γ 2 − ) and splits them into two or three pairs of quasi-energy levels. The frequency of the test pulse is in resonance with the frequency Γ 5 + of the exciton. The corresponding intensities for various directions of the electric vector of the pump field E L, the polarization vector ξ, and the wave vector q of the test pulse are obtained. The frequency of the quantum beats is twice the Rabi frequency, which for different values of E L, ξ and q contains different sets of matrix elements of the dipole transitions between the levels 1s(Γ 5 + ) and 2p(Γ 4 − ,Γ 5 − ,Γ 3 − Γ 2 − ). Thus, by measuring the period of the quantum beats it is possible to determine the unknown matrix elements of the indicated transitions.
The quantum beats (QB) in the time-dependent absorption intensity of the probe pulse and the spontaneous luminescence one in Cu2O crystal at the condition of double optical resonance are studied theoretically. It is assumed that the pump is performed by the CO2 laser pulse, which couples dynamically the 1s (Γ 5 + ) and 2p (Γ 4 - , Γ 5 - , Γ 3 - , Γ 2 - ) excitonic states and leads to their splitting into two or three quasienergy levels. The frequency of the probe pulse is in the region of the Γ 5 + exciton resonance. The respective intensities for different directions of the electric field E L of the pump, the polarization ξ of the probe pulse, and the observation q are obtained. The QB take place with the doubled Raby frequency, which at different E L , ξ, and q includes different sets of matrix elements of dipole transitions between 1s (Γ 5 + ) and 2p (Γ 4 - , Γ 5 - , Γ 3 - , Γ 2 - ) levels. These unknown matrix elements can be obtained, measuring the period of the QB.
Abstract A semiclassical exciton-biexciton model for CuCl is used to obtain the stationary solutions for optical bistability (o.b.) by numerical integration of the second-order Maxwell equation in the limit of large Fresnel numbers. The results obtained from the calculation, which we call exact (ex.), are compared with corresponding numerical results by using the slowly varying envelope approximation (s.v.e.a.) as well as corresponding analytical results obtained by using the mean-field approximation (m.f.a.). The results obtained with the s.v.e.a. are shown to be in close quantitative (within 5%) agreement with the ex. results for each point in the parameter space considered, whereas the m.f.a. gives reasonably good qualitative results only (more than 20% quantitative discrepancy with ex.). Furthermore, o.b. is predicted from these calculations for incident laser field detunings on either side of the two-photon biexciton resonance as well as in the neighbourhood of the resonance. The nonlinearity in the dielectric function that causes o.b. is seen to be very nearly of the Kerr medium type, and consequently, the two-photon biexciton resonance contributes only weakly to the o.b. characteristics.