Non-linear optical properties of excitonic complexes in prolate ellipsoidal quantum dot

This study presents a theoretical study of ground-state exciton and biexciton properties in strongly prolate ellipsoidal GaAs quantum dot. Using a variational approach with trial wave functions constructed from single-particle states, we examine the dependence of exciton and biexciton energies on the dot’s geometric parameters. The oscillator strengths of exciton–biexciton transitions are analyzed as functions of the major and minor semiaxes. We further investigate the third-order optical susceptibility near single- and two-photon resonances, elucidating the role of exciton–biexciton interactions. The results show that one-photon resonances dominate the nonlinear response, with contributions exceeding those of two-photon resonances by approximately four orders of magnitude. Absorption coefficients for exciton and biexciton transitions are evaluated for a fixed major semiaxis and varying minor semiaxis, along with the biexciton two-photon absorption coefficient. Finally, we analyze biexciton-induced nonlinear refractive index modulation, which exhibits a sign reversal across resonance and a pronounced peak–dip structure, indicating strong dispersive behavior and significant excitonic phase modulation.