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Rotation dynamics of particles trapped in a rotating beam.

The rotation dynamics of particles trapped in a rotating beam is theoretically investigated. We find that there is a critical angular speed for the rotating beam. If the angular speed of the rotating beam is smaller than the critical value, the angular velocity of the trapped particle is nearly the same as that of the rotating beam, which is in accord with existing experimental observation. Otherwise, the angular velocity of the trapped particles will become periodic or quasi-periodic with time, depending on the beam polarization, which, to the best of our knowledge, has not been previously reported. Moreover, we also propose some methods to determine the ratio between the beam power and the maximal angular speed of the trapped particle, which can be used to estimate the minimum power required to rotate the particle at a given angular speed.