Position-dependent Effective Mass and Intense Laser Field Effects on Nonlinear Optical Properties of GaAs/AlxGa1−xAs Asymmetric Coupled Cylindrical Quantum Well Wires

A systematic theoretical investigation is presented for the nonlinear optical properties of GaAs/Al0.3Ga0.7As asymmetric coupled cylindrical quantum well wires (CCQWWs) incorporating, for the first time in this geometry, the full position-dependent effective mass (PDM) through the BenDaniel–Duke kinetic-energy operator, combined with a systematic comparison against the widely used constant-mass approximation. A non-resonant intense laser field (ILF) is treated within the non-perturbative Floquet dressed-potential approach, and the three lowest-order nonlinear optical susceptibilities — optical rectification (NOR, χ(2)), second-harmonic generation (SHG, χ(2)), and third-harmonic generation (THG, χ(3)) — are computed via the compact density-matrix formalism. The ILF is found to reshape the double-well confinement potential dramatically: the THG peak amplitude is enhanced by up to 148-fold at α0=6 nm relative to the field-free case, arising from a two-photon intermediate resonance (ħω≈E31/2=33 meV at α0=6 nm) that drives the intermediate-state denominator D2 near zero. The NOR amplitude decreases overall with α0 (with a small local increase at α0=4 nm) due to ILF-induced suppression of the off-diagonal matrix element M13, while SHG reaches a 3-fold maximum at α0=4 nm. The PDM introduces corrections of up to 34% in the THG coefficient and up to 1.1 meV in the transition energies relative to the constant-mass approximation, with the sign and magnitude of the correction depending sensitively on α0.