<p>Tunneling of charge carriers can reveal the relaxation mechanism of electronic quasi-bound states under the quantum-confined Stark effect. In this study, the authors used open boundary conditions to solve the laser-dressed Schrödinger equation under a high-intensity regime electric field. The Finite Element Method, utilizing the position-dependent effective mass approximation, was employed to determine the electronic quasi-bound states of a GaAs_0.75Sb_0.25/GaAs semi-V-shaped quantum well and their complex envelope wavefunctions. The quasi-bound energy levels and tunneling times of a heavy hole were derived from the real and imaginary components of complex eigenenergies, respectively. The intra/valence-band linear and third-order nonlinear optical characteristics were analyzed using the density matrix formalism, considering a two-level system and intersubband relaxation rate defined based on the Matthiessen rule. The results indicated the appearance of the tunneling phenomenon for electronic quasi-bound states with finite lifetimes when subjected to electric fields in a high-intensity regime. This was in contrast to bound states with infinite lifetimes under low-intensity regime electric fields. Electronic studies also showed more significant tunneling effects for high-intensity electric fields when the laser field was active. Optical spectra under all electric fields displayed red shifts associated with the reduced energy differences between the ground and first excited states following the application of a non-resonant intense laser field. The linear optical absorption coefficients exhibited a weakened resonance when the laser field was activated, but an increase was observed in other optical responses. These findings suggest exciting possibilities for the design and development of optoelectronic devices with customized optical properties.</p>