Morphological Tracking\nand Tuning of Silica Nanoparticles\nin Optomechanical Systems for Enhanced Stable Levitation in Vacuum

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