212 6.3  Optical Force Tools

FIGURE 6.1  (See color insert.) Optical tweezers. (a) The sum of refractive forces through a bead in optical tweezers

results in a net force roughly toward the laser focus. (b) Many biomolecules have a strong absorption in the visible light

range, illustrated here with chlorophyll in plants and hematin in the blood; water absorbs weakly in the visible region,

increasing absorption in the near infrared, but with a local dip in absorption at ~1 μm wavelength. (c) Typical arrangement

of beam steering (and expansion) for optical tweezers. (d) Two (or more) optical traps can be generated by time-​sharing

of the laser beam using rapid deflection by an AOD.