Large Four-Wave Mixing of Spatially Extended Excitonic States in Thin GaAs Layers

Abstract

We study the size dependence of the nonlinear response of weakly confined excitons for the size region beyond the long wavelength approximation regime. The observed degenerate-four-wave mixing signal of GaAs thin layers exhibits an anomalous size dependence, where the signal is resonantly enhanced at a particular thickness region. The theoretical analysis elucidates that this enhancement is due to the size-resonant enhancement of the internal field with a spatial structure relevant to the nondipole-type excitonic state. These results establish the formerly proposed new type of size dependence of nonlinear response due to the nonlocality induced double resonance.

Generation of entangled-photon pairs from biexcitons in CuCl thin films: Nano-to-bulk crossover regime

“…On the other hand, the scattering spectra of the thin film are significantly modified from the bulk ones, and we found that they reflect the exciton-photon coupled modes in the thin film. 17,18,21,33,35 Therefore, the RHPS measurement is also useful to observe the exciton-photon coupled modes in nano-structured materials 34 as well as the four-wave mixing 17,29,35 and the two-photon excitation scattering. 33 We also found that semiconductor thin films have much degrees of freedom to control generated states of entangled photon pairs.…”

“…11,50-52 Moreover, optical responses explicitly reflects the confinement of center-of-mass motion of excitons in nano-structured materials and also in the nanoto-bulk crossover regime, [17][18][19][20][26][27][28][29][30][31][32][33][34][35][36] which we investigate in the present paper.…”

“…Actually, owing to the recent development of nanoscale fabrication, anomalous nonlinear optical processes have been reported in semiconductor nano-structures and in the nano-to-bulk crossover regime. 17,[26][27][28][29][30][31][32][33][34][35][36] Further, it shows a rapid radiative decay rate of excitons on the order of 100 fs due to the exciton superradiance.…”

Radiative coupling of A and B excitons in ZnO

“…Accordingly, a wave-wave coupling between excitons and radiation occurs, and their interaction volume becomes considerably larger, especially for multipole-type excitons with the CM quantum number λ ≥ 2, leading to large radiative corrections. As a result, the nonlinear optical responses are enhanced [29][30][31] , and the level shift and radiative decay rate are resonantly increased [32][33][34] with the sample size. We should note that such a large interaction volume also strengthens the coupling between different components of excitons via radiation.…”

“…The real part Re[ ω ξ ] gives the eigenenergy including the radiative shift and the imaginary part −Im[ ω ξ ] gives the radiative width. An increase in the film thickness leads to a large interaction volume between excitonic waves and radiation waves, and their phase-matching leads to the large radiative correction from the bare excitonic states especially in a nano-to-bulk crossover size regime [30][31][32][33][34] .…”