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. Author manuscript; available in PMC: 2018 Jan 1.
Published in final edited form as: Methods Mol Biol. 2017;1486:483–509. doi: 10.1007/978-1-4939-6421-5_19

Figure 3.

Figure 3

Dual-beam optical trap layout. A 1064 nm wavelength laser passes through a half-wave plate and then the beam is separated into two beam paths (i.e., two traps) by a polarizing beam splitter. The two independent beams can then be independently steered by acoustic-optical deflectors (AODs) before being recombined by a polarizing beam combiner. Diffraction-limited optical traps are formed in the focal plane by a water immersion objective. After interacting with the beads, the laser light is collimated by a condenser lens, and the polarized beams are collected separately on two quadrant photodiodes (QPDs). The deflection of the laser beam on the QPDs reports the magnitude of the force on the beads, which can be converted to distance by dividing by the trap stiffness. Figure is adapted from (23).