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3.2 Theoretical Analysis 91
(a) (b)
w' R
r r m
n q1(r)
R
b m -1
f(r)
f(r) Fg f
s
O w
w
f F m f(r)
Fs
Y
O b
X 1
Y
Z Z Z
Fig. 3.11. Geometry for calculating axial trapping efficiency of polystyrene mi-
croshere. The laser focus is on the optical axis which is parallel to the center line of
the microsphere [3.4]

(a) (b)
W
r
R m W R m n
q
b 1
A
n
R cotF R
m m q 1 Fg
A
F m g
O
a f ' s'
W'
-1 f g O b 1 Y
X
Y
Fs
Z
Z
Fig. 3.12. Geometry for calculating the transverse trapping efficiency of polystyrene
microshere. The laser focus is located along the transverse center line of the sphere
[3.4]

(a) Trapping efficiency (b) 0.4
-0.4 -0.2 0 0.2 0.4 0.3
Focus point Trapping efficiency 0.2

0.1
0 Y
0 0.2 0.4 0.6 0.8 1.0
Z
Focus point
Fig. 3.13. Total trapping efficiency Q t exerted on a polystyrene microsphere sus-
pended in water by trap with a uniformly filled input aperture of NA = 1.25 for
axial (a), and for transversal (b)directions