The focusing behavior of an azimuthally polarized, axisymmetric Bessel-modulated Gaussian (QBG) beam through dielectric interface using vector diffraction theory in a high-numerical-aperture system. The results indicate that the intensity pattern in the focal region can be significantly controlled by the beam parameter ????. In contrast, the parameter ???? strongly affects the axial intensity distribution. Changes in this parameter can lead to focal splitting and a controllable shift of the focal position, while a real value of ???? may also produce a local minimum in intensity. For certain conditions, increasing the imaginary component of ???? reduces the size of the transverse focal spot while simultaneously increasing the full width at half maximum of the axial intensity profile. These results demonstrate the QBG beam as a highly tunable structured light field capable of precise focal engineering. The ability to control focal morphology and depth highlights its potential for applications in high-resolution microscopy, optical trapping, precision material processing, optical data storage, deep-tissue imaging, optical coherence tomography, and customized optical system design.
