Biexcitonic Effect on Transient Nonlinear Refraction and Absorption in CdS Quantum Dots
Swati Goyal and Pranay K. Sen
Transient optical nonlinearities of semiconductor quantum dots in the strongly confined regime are studied, in which the exciton, biexciton and quantum confinement effects are taken into account. The time dependent perturbation technique for a three-level system, under the near band gap resonant excitation regime, has been employed. The relaxation and dephasing mechanisms are incorporated phenomenologically. The induced polarization is calculated from where the real and imaginary parts of the third-order nonlinear optical susceptibility, responsible for the occurrence of nonlinear refraction and nonlinear absorption respectively, have been derived. The temporal and detuning spectra of nonlinear refraction and absorption and their dependence on density and binding energy of biexcitons have been analyzed. The results agree qualitatively well with the experimental observations in small CdS quantum dots.