Visualization 5-Optical tweezer experiment with laminar flow.mp4

Visualization 5 shows the QPD signal and the particle motion image of 500 nm PS sphere measured in a uniformly flowing solution at a linear velocity of 16.6 μm/s (trapping beam is 976 nm and optical power is 30 mW). It can be seen that the PS sphere is moving at a uniform speed in the horizontal direction, and the trap region (potential well) is marked as a yellow circle. When the PS spheres are in the vicinity of the potential well, they are stably trapped for a while and then escaped due to the flow velocity. Corresponding to the QPD signal curve on the left is: when a particle is trapped by optical tweezers, the QPD signal is in the form of jump signal generation. The trap details in the deformed potential well have been shown in the QPD signal in FIG. 5(b) of the text, when particle entering the potential well with presence of a laminar flow, the QPD signal jumps quickly from the upstream side to the downstream side of the trapping beam, then randomly walking at the bottom position of the skewed potential well for a period (signal fluctuation at the bottom position), and finally escape (signal returns to the beam centre). In this paper, several trap experiments were carried out by diluting the particle concentration, controlling the flow velocity of solution and changing the laser power to compare the influences of different conditions to trapping time