Theoretical Research of Optical Pulse Response of Quantum Confined Excitons

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We have developed the theory for the optical response of the ultra short pulse in which the nanoscale spatial structure of the response field in the media is correctly considered. This theory has following features.The nonlocal response is considered.The microscopic position dependences of the induced current density and the response field are correctly taken into account.The self-consistency of the induced current density and the response field are taken into account.Nonlinear response can be treated.We take the method such that the simultaneous equations of Maxwell eq. and the equation for the density matrix of the matter system are numerically solved. Taking the rotating wave approximation and slowly varing envelope approximation in time, and reducing the number of the exctitonic states as bases, we make this calculation feasible. Appling this method to the ultra thin film confining excitons, we have clarified the following points.1.The remarkable nanoscale spatial structure of the response field appears even for the short pulse of several hundreds femto second, and the selection rule that should hold in the case of long wavelength is broken for both the linear and nonlinear regimes. We understand that our approach is essentially necessary in such conditions.2.We elucidate, for the first time, the real time characteristics of the internal field by the short pulse undergoing multiple reflection.3.The time characteristics of the nonlinear signal reflects the above mentioned motion of the internal field in time, thus, the nano-scale spatial structure of the internal field takes a important role in the time characteristics of the nonlinear response. It is also clarified that if we neglect this spatial structure of the internal field, we can not describe the correct time variation of the nonlinear signal at all.