Building an optical tweezers
Working principle of optical tweezersFrom the change of beam directions shown in the Fig. 1, it can be seen that the beam’s momentum in the propagation direction become bigger after passing through the particle. That means the light beam gains momentum in the propagation direction. According to the conservation law of momentum, the particle is imparted a momentum backward.
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Some consideration in the designAccording to the working principle of optical tweezers, the diameter of the incident beam should be as large as possible. So it is necessary to determine the maximum beam diameter which can be coupled into the objective. Fig. 2 shows a simple way for the determination of this dimension, which will be as the base for selecting the two lenses for the laser beam expander.
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Video of the particle trapped by the optical tweezers |