FIGURE 2.

A schematic illustration of the force-measuring optical tweezers setup. A continuous-wave Nd:YAG laser is used for trapping. The trapping position is controlled by a set of lenses and mirrors. The light is introduced via a dichroic mirror coated for high reflection of 1064 nm light and high transmission of visible light. The probe-laser light is produced by a fiber-coupled HeNe laser focused in the proximity of the trapped bead and imaged by the microscope condenser onto a position-sensitive detector (PSD). The sample is placed on a custom-made slide holder mounted in a piezo stage. A detailed description is given in Andersson et al. (11).