Understanding the libration spectra of levitated nanodumbbell rotors

Abstract

Shoulder-like features are often observed in the libration power spectral density of optically levitated nanodumbbell rotors, yet their origin remains unclear. By modeling both deterministic and thermal torques in realistic optical fields, we identify the mechanism responsible for these spectral signatures. We show that these features arise from the interplay between confined libration of the particle intermediate axis and thermally driven rotations about the particle's symmetry axis.