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6 Answers, Hints and Solutions 219
A3.6 See Fig. A.4.

1.2

1.0
0.8
0.6

0.4
RADIUS
E´
0.2
E
0 Y
0.2 Z
0.4

0.6
0.8
1.0

1.2
Fig. A.4. Magnitude and direction of total trapping efficiency (optical pressure
force)for a microspore of relative refractive index of 1.2 at arbitral focal position in
the yz plane. A circularly polarized laser beam uniformly fills the objective aperture
of NA = 1.25 [6.4]

A3.7 The discrepancy between theoretical and experimental results comes
from the fact that the trappingposition moves upward due to the gravitational
force, which decreases Q t as shown in Fig. A.5. Expected trajectory of the
trapping(focus) position in the polystyrene are shown by 1: for a diameter

0.4
trans 0.3
Predicted Q max 0.2

0.1
0
0 10 20 30 40 50
Particle diameter (mm)
trans
Fig. A.5. Dependence of predicted Q max on sphere diameter for polystyrene, which
trans
is derived from experimental data of Fig. 3.32. Q max decreases as diameter increases