Capture region shrinkage and levitation instability of optical trap induced by decreased damping in vacuum

Oscillators based on levitated particles in high vacuum are a promising technique for realization of ultrasensitive detectors for precision force sensing. Direct particle loading under high vacuum is made difficult by decreased damping, which causes particle to escape during vacuum pumping. Theoretical investigations of the capture regions of optical traps in vacuum are necessary for developing new loading methods and improving loading efficiencies. We define an effective capture region (ECR) as a criterion for capture of particles, whose initial condition can be considered as the equivalent to a later-in-time situation of the actual trajectories. Quantitative analyses of the effective capture region (ECR) based on particle dynamics show that the ECR shrinks drastically at specific pressure interval. This shrinking interval is consistent with the experimental escaping pressure, indicating the nanoparticle escape mechanism. •A method to quantitatively characterize capture regions of optical trap is proposed.•Nanoparticles in optical trap tend to escape at a certain pressure interval.•Drastically shrinkage of ECR can explain pressure-related escape mechanism.