Understanding thermal induced escape mechanism of optically levitated sphere in low vacuum

The escape phenomenon, mainly caused by thermal effects, is known as an obstacle to the further practical application of optical levitation system in vacuum. Even though thermal effects have been mentioned in many works, the escape mechanism of heated particle remains unclear. Irregular photophoresis induced by thermal effects can act as an “amplifier” of Brownian motion. Studies on this topic provide interpretation for particle escape phenomenon during vacuum pumping, as well as valuable insights into the micro- and nanoscale thermal effects in optical trap in vacuum. In this paper, we derive and test a dynamic model for the motion of an optically levitated particle in a non-equilibrium state and demonstrate the escape mechanism. The result of theoretical investigations is consistent with experimental escape at 0.1 mBar.