“…The frequency of one beam is shifted by a mount of 110 MHz using an acoustooptic modulator (AOM), and then it is combined with the other laser beam (the frequency is not shifted) on a PBS to avoid the interference of the two trapping beams. Then the two beams are tightly focused by a high NA objective lens (Nikon CF Plan 100X, NA=0.95) in the vacuum system [53,54]. The directivity of one beam is precisely controlled by a motor-driving mirror.…”