  When introducing a nanoparticle into an optical trap, its mass and shape are
not immediately apparent. We combine a charge-based mass measurement with a
shape determination method based on light scattering and an analysis of the
damping rate anisotropy, all on the same set of silica nanoparticles, trapped
using optical tweezers in vacuum. These methods have previously only been used
separately, and the mass determination method has not been applied to
asymmetric particles before. We demonstrate that the combination of these
classification techniques is required to distinguish particles with similar
mass but different shape, and vice versa. The ability to identify these
parameters is a key step for a range of experiments on precision measurements
and sensing using optically levitated nanoparticles.
