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120 3 Optical Tweezers
bringparticles from a reservoir and pattern nanoparticles on the substrate.
Fixingwas carried out usingopposite charges [3.40] or local photopolymer-
ization [3.41] around the nanoparticle assembly.

Optical Rotor

Optical pressure can also rotate dissymmetrical microobjects. Many types
of optical rotor have been proposed for future applications, which will be
described in Chap. 4.

Problems

3.1. Explain the method of measuringan optical pressure force.

3.2. Explain the procedure how to simulate the trappingforce exerted on a
microsphere illuminated by a converging laser beam.

3.3. Compare the axial trappingefficiencies for a microsphere predicted by a
straight ray with a parabolic ray.
3.4. Calculate the transverse trappingefficiency for a microsphere when the
focus of the uniformly input laser beam is located alongthe transverse center
line (perpendicular to the optical axis) of the sphere.

3.5. Compare the transverse trappingefficiency for a microsphere predicted
by a straight ray with a parabolic ray.

3.6. Calculate the total trappingefficiency for a microsphere when the focus
of the input laser beam is located at arbitral positions in the sphere.

3.7. Consider the reasons for the transverse trappingpower discrepancy be-
tween the theoretical prediction and the experimental result. Show the tra-
jectory of the trapping(focus) position in the sphere.