Biomedical Engineering Reference
In-Depth Information
Fig. 1.10.
Thewavevectordistributionofthefocusedbeam
Fig. 1.11.
The relations among
k
m
,
k
1
,
k
1
,and
k
2
axis of the lateral direction, and
η
is the axis parallel to the optical axis. In
Fig. 1.10 one section is shown, because it is symmetrical about the
η
-axis.
If the vector
k
m
is defined by
k
1
−
k
2
,
k
m
≡
k
1
+
(1.2)
it can take many kinds of combinations of
k
1
,
k
1
,and
k
2
, because each wave
k
1
,and
vector of
k
1
,
k
2
has a distribution like that shown in Fig. 1.10 (see
Fig. 1.11).
The gray region in Fig. 1.12 shows the available
k
m
. The observable
wave vector of the yielded CARS is also expressed by Fig. 1.8 and drawn
in Fig. 1.12 by an arc of a circle. The phase-matching condition is satis-
fied with the crossing of
k
m
and
k
3
.Itisfoundthattheavailableregionof
k
m
is so wide as to cross
k
3
. Hence, the phase-matching condition is easily
satisfied.
The above phase-matching condition is the result of the isotropic sample.
To estimate the imaging properties, it is necessary to take into consideration
the effect of diffraction. The effect of diffraction will not be discussed here
(the detailed discussion was described in reference [21]), but only the result
will be described.
Figure 1.13 shows the cutoff frequency of the transfer function of CARS
microscopy with a confocal configuration. The cutoff frequency of the trans-
