We propose a method for accurately controlling the orientation of ellipsoidal particles in three-dimensional space with arbitrarily polarized vector beams. By conducting theoretical modeling and simulations, we explore the optical force distribution, potential well characteristics, and orientation dynamics of ellipsoidal particles with specifically polarized vector beams. Traditional optical tweezers have limitations when manipulating non-spherical particles like ellipsoids. However, our method overcomes these challenges, providing precise and stable control of ellipsoidal particles. The results not only demonstrate the feasibility of trapping ellipsoidal particles at the focal point but also reveal a direct relationship between the polarization direction of the trapping beam and the spatial orientation of the particles. This manipulation has significant implications, thus providing technical support and a theoretical foundation for advances in micro-nano technology, biomedical research, and nanomaterials. Potential applications include drug delivery, biosensing, and nanofabrication fields, where precise control of particles enables innovations.

In the theoretical model, the optical field in the focal region of a vector beam with arbitrary polarization can be derived by adopting dipole inversion and the Richard-Wolff vector diffraction theory. Theoretical calculations reveal the distribution of optical forces on ellipsoidal particles under different vector beams, including gradient forces, radiation, and spin torque. By applying the Clausius-Mossotti correction theorem, we derive the expression for the electric polarizability of anisotropic ellipsoidal particles in the local coordinate system. Additionally, a rotation matrix transforms the particle’s polarizability from the local to the laboratory coordinate system, thereby ensuring an accurate representation of the interaction between the optical field and the particle. In the simulations, we analyze the optical field distribution, including intensity and polarization, of vector beams with varying polarization and their effects on trapping ellipsoids. The optical force distribution on ellipsoidal particles under different vector beams with varying polarization is examined, with a focus on the magnitude and direction of transverse and longitudinal forces. Meanwhile, the optical potential well depth is calculated to assess the conditions for stable trapping. Additionally, the torque and rotation of the ellipsoidal particles are studied, revealing their three-dimensional orientation and the relation to the polarization direction of the incident light.

We calculate the optical forces, including the gradient and radiation forces, which act on ellipsoidal particles trapped by arbitrarily polarized vector beams. Notably, the gradient force is the primary mechanism for trapping ellipsoidal particles, while the radiation force effect is minor. At the focus, optical forces create a three-dimensional equilibrium, with the transverse force drawing the particle toward the focus and the longitudinal force ensuring symmetry for stable trapping. By calculating the optical potential well depth, we find that optical fields with various polarizations can create deep wells, counteracting Brownian motion and enabling stable trapping. Simulations show that stable trapping of ellipsoidal particles is possible, regardless of the beam’s polarization direction. In analyzing the optical forces acting on ellipsoidal particles, it is essential to examine how the particles are trapped at the minimum of the potential well and to understand how the optical torque affects their orientation in three-dimensional space. The results show that when beams with arbitrary polarization are employed to trap ellipsoidal particles, the optical forces can trap the particles at the focal point, and the spin torque aligns the ellipsoidal particle’s major axis with the polarization direction. By adjusting the polarization of vector beams, including polar and azimuthal angles, precise three-dimensional orientation control of the particles can be achieved. The spin torque aligns the particle’s major axis with the polarization direction, which leads to stable orientation. The results not only deepen our understanding of the particle trapping dynamics at the nanoscale but also provide theoretical support for the development of more efficient optical manipulation techniques.

First, we adopt the dipole back-propagation theory to derive the field distribution of vector beams with arbitrary polarization in the focal region. Then, we calculate the optical forces and potential well distributions that govern the trapping of ellipsoidal particles with specific polarization. The results show that the vector beams in our study can stably trap ellipsoidal particles at the focal point. Furthermore, we investigate how the spatial orientation of ellipsoidal particles’ under stable trapping relates to the polarization direction of the trapped beam. Our results show that under stable trapping, the spatial orientation of ellipsoidal particles aligns completely with the polarization direction of the trapped light. This suggests that by designing the incident light beam, we can achieve precise orientation control of ellipsoidal particles. Therefore, our research has great potential to advance micro-nanotechnology, biomedicine, and nanomaterials, opening up new opportunities for innovation in these rapidly evolving fields.