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.
We investigated the third-order nonlinear response of excitons in GaAs thin films grown by molecular beam exitaxy. Degenerate four-wave mixing (DFWM) measurements were made using picosecond pulses of 3.2 ps auto correlation width at T=5 K. The DFWM signal of a 110-nm-thick GaAs film at exciton resonance energy is 25 times larger than that of a 1-μm-thick GaAs film. This enhancement is explained by the confinement effect of exciton polaritons, which is due to the nonlocal response of the center-of-mass quantized states of excitons in a radiation field.
An optical Kerr signal has been simulated for GaAs/AlAs multilayer cavity structures by using the self-consistent transfer matrix method. Enhancement of the Kerr signal intensity was clearly demonstrated for the cavity mode (λ∼1504 nm) owing to the strong optical field in the multilayer cavity. The Kerr signal intensity can be further enhanced with the use of a higher nonlinear refractive index only for the half-wavelength (λ/2) cavity layer. We propose a GaAs/AlAs multilayer structure with the λ/2 cavity layer containing InAs quantum dots embedded in strain-relaxed barriers for an ultrafast optical Kerr gate switch with extremely low switching energy.
GaAs/AlAs coupled multilayer cavity structures are proposed as terahertz emission devices. Two cavity modes with an optical frequency difference in the terahertz region can be realized when two cavity layers are coupled by an intermediate distributed Bragg reflector multilayer. Interference between the enhanced light fields of the cavity modes has been demonstrated by the simultaneous injection of two cavity-mode lights using an ultrashort pulse laser. Such coupled multilayer cavity structures are promising for use as compact and room temperature operable terahertz emission devices based on difference frequency generation by the cavity-mode lights.
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