Figure 2.

Schematic diagram of the optical tweezers setup. The original laser beam is split by a PBS into two beams, which are independently controlled through movable mirrors, telescopes, and an AOD. The beams are jointly focused into the sample cell through a microscope objective. A photodetector in the back focal plane is used to measure the fluctuations of a trapped microsphere for calibration purposes. Two CCD cameras record brightfield images of the sample. One CCD camera is used to measure the axial position of the trapped microsphere, and the other is used to compensate for drift in real time.