Biomedical Engineering Reference
In-Depth Information
(a)
(b)
(c)
(d)
(e)
Figure 17.12 AO microscope loop correction steps. (a) An uncorrected image of the luorescent microsphere.
(b)-(e) Result of closing the loop by using a loop gain factor of 0.4. he length of the bar in (c) is equal to the dif-
fraction limit of the 40× (0.75 NA) objective lens, 0.45 μm. he bead was located 100 μm beneath the surface of the
embryo.
Wavefront 1
DM Shape
14
14
20
20
12
12
10
10
10
10
8
0
8
0
6
6
- 10
- 10
4
4
- 20
- 20
2
2
2
4
6
8
10
12
14
2
4
6
8
10
12
14
X (Apertures)
(a)
X (Apertures)
(b)
Figure 17.13 (a) Initial wavefront measurement. (b) Closed-loop DM wavefront. he legend is scaled in percent
wavelength at 650 nm.
I
I
peak,e
(17.7)
S
=
relative
peak,a
Figure 17.13 shows the initial wavefront measurement (wavefront before correction loops started)
and the inal shape of the DM for the adaptive loop corrections seen in Figure 17.12. he DM shape was
obtained by summing the shape commands that were sent to the DM for each loop step. he small steps
in voltage reduce the nonlinear efects from the DM since only small changes in the mirror surface are
produced for each time step. here was a 30 nm RMS error diference between the inal DM shape and
the original wavefront measurement. he inal error between these measurements can be partly attrib-
uted to the wavefront reconstructor. he efect comes from the lack of measurements outside the edge
of the aperture (Poyneer, Gavel, & Brase 2002). he DM wavefront is inverted to help comparison of the
wavefront error and the mirror shape.
17.2.4 The Isoplanatic Angle and Half-Width
he isoplanatic angle is a relative measure of the FOV over which the AO system can operate and is
deined as (Hardy 1998)
(
) =
2
σ
θ 2
=
ϕ
(
X
, )
0
ϕ
(
X
,
θ
)
1 rad
2
(17.8)
0
 
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