Morphological Tracking and Tuning of Silica Nanoparticles in Optomechanical Systems for Enhanced Stable Levitation in Vacuum

Optically levitated nanomechanical resonators in vacuum have attracted widespread attention for their ultrahigh sensitivity for mechanical quantities by overcoming the limitations of clamped resonators. Although commonly utilized amorphous silica nanoparticles (NPs) exhibit low absorption and high transparency, they still face challenges to survive levitation in high vacuum environments for unclear reasons. By monitoring the physicochemical properties such as scattering, motion, mass, size, and density of silica NPs during the pumping process, we speculate that the loss of NPs from optical traps may arise from the motion instability induced by laser heating at a low air pressure. In this work, two types of NPs undergo heat treatment between 100 and 1200 °C to release impurities before being loaded into an optical trap. The surviving ratio of stable levitation for both types of NPs in high vacuum significantly increases after heat treatment. In particular, for NPs heated to 600 °C, the surviving ratio, respectively, improves from Approximately 30%–100% and Approximately 0–81% for two types of NPs. The loss mechanism is further confirmed by the relatively stable physical parameters for heat-treated NPs levitated in an optical trap during the air pumping process. This work paves the way for the wide application of levitated nanoresonators and indicates that levitated optomechanical systems could be a promising tool for studying the dynamics and in situ behavior of small particles like biogenic and atmospheric aerosols and space dust.