Optically levitated systems pioneered by Arthur Ashkin have emerged as a powerful platform for physics and bioscience research owing to their non-contact and non-invasive nature. In vacuum, such systems offer exceptional isolation from environmental noise and enable controlled suppression of decoherence from background gas, making them a focus in fundamental physics and precision measurement. Notable achievements include ground-state cooling of the center-of-mass motion. Furthermore, compared to cantilever-based optomechanical systems, these systems exhibit richer physical phenomena, such as observed libration and GHz rotation of anisotropic levitated particles.

However, the polarization characteristics of the scattered field from an optically levitated anisotropic particle remain poorly understood—critical for motion manipulation, detection, and cooling. Here, we present a theoretical study of these characteristics for an intrinsically isotropic ellipsoidal particle driven by linearly or circularly polarized laser light. We first calculate the far-field distributions of the scattered field and then numerically evaluate the signal amplitudes for libration and rotation from the interference field, as detected by a collection lens positioned perpendicularly to the trapping laser axis.

Our analysis reveals several counterintuitive results. The libration signal amplitude is minimal when the collection lens is centered on the beam axis and increases as the lens is displaced off-axis. Moreover, the signal can be increased when the half-wave plate rotating by a appropriate angle. Meanwhile, the \beta rotation signal is detectable. By measuring a specific polarization component of the interference field, we find that the signal amplitudes for the \alpha and \beta rotation are not maximal on-axis but instead reach their maxima in the four quadrants of the transverse plane.

This work establishes an important foundation for the manipulation, detection, and cooling of optically levitated anisotropic particles in a vacuum.