Intense laser field effects on second harmonic generation in double coupled elliptical quantum wires: the role of geometric orientation

Abstract In this study, the effects of an intense laser field (ILF) on the electronic structure and nonlinear optical properties of double coupled elliptical quantum well wires (DEQWW) are investigated theoretically. Calculations are performed using the effective mass approximation and the diagonalization method. To elucidate the impact of geometric orientation, two different models are considered: in Model A, the right EQWW is positioned horizontally, whereas in Model B, the same well wire is rotated by 45°. The findings demonstrate that increasing the intensity of the applied laser field causes significant distortion in the confinement potential and leads to splitting at the bottom of the potential wells. This structural modification facilitates the delocalization of electronic wave functions and enhances tunneling probabilities, thereby strongly altering the intersubband transitions and dipole moment matrix elements (DMMEs). Notably, for dressing parameter values of $$\alpha_{0}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>α</mml:mi> <mml:mn>0</mml:mn> </mml:msub> </mml:math> &gt; 5 nm, a dramatic increase in the second harmonic generation (SHG) coefficients is observed, accompanied by the widening and shallowing of the potential profiles. Interestingly, although Model B is geometrically more sensitive to the ILF effect and promises larger DMMEs, Model A exhibits unexpectedly slightly higher SHG amplitudes. This is attributed to the ``near-resonance" condition, where the ( $${\text{E}}_{21}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mtext>E</mml:mtext> <mml:mn>21</mml:mn> </mml:msub> </mml:math> ) and ( $${\text{E}}_{31}/2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mtext>E</mml:mtext> <mml:mn>31</mml:mn> </mml:msub> <mml:mo>/</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:math> ) transition energies become proximal in Model A. Furthermore, a distinct transition from blue-shift to red-shift in the optical spectrum is detected with the variation of the ILF parameter. These results suggest that by simultaneously tuning the laser field intensity and geometric orientation, the optical response of nanostructures can be optimized, making them suitable candidates for tunable photonic devices. Graphical abstract