Biomedical Engineering Reference
In-Depth Information
generate an SA allowing superresolved imaging by a simple digital FT of the information
contained in the SA. Figure 9.6 depicts the SA generation incoming from the addition of
the elementary apertures. In addition, we have also considered a second illumination ring
incoming from a higher value of the oblique illumination angle which can be implemented
by considering a wedge prism having a higher deviation angle.
To experimentally validate this second SALDHM approach, we first present initial
calibration using a negative USAF resolution test target. Here, the test target must be
negative instead of positive in order to break the Gabor's regime. For that experiment, we
have used an He
Ne laser (632 nm emitting wavelength) as our illumination source, a
CCD (Basler A312f, 582 3 782 pixels, 8.3
m pixel size, 12 bits/pixel) as our imaging
device, a wedge prism with 10 deviation angle as the illumination prism for the first
illumination ring (NA ILUM 5 0.17), a beam splitter cube (20 mm 3 20 mm side, BK7) to
allow holographic recording, and a doublet lens (80 mm focal length and 60 mm diameter)
to provide a spherical divergent off-axis reference beam. Optic mounts, beam expanders,
neutral density filter wheels to equalize the beam aspect ratio, and micrometric translation
stages complete the experimental setup.
μ
The test target is placed at 36 mm in front of the CCD but the presence of a beam splitter
cube brings its image through it closer to the CCD. Under paraxial approximation, the
displacement
Δs 5 e (1 2 1/ n ), where e
and n are the width and the refractive index of the plate, respectively. Since the refractive
Δs originated by a plano-parallel plate is given by
Initial pupil system (CCD aperture):
(
Δ x ,
Δ y ) WIDTH
Off-axis frequency bands provided
by the first illumination ring
5 Δ y
Off-axis frequency bands provided
by the second illumination ring
First off-axis illumination ring
Second off-axis illumination ring
4 Δ y + Δ x
Figure 9.6
Hypothetical SA incoming from the addition of eight off-axis elementary apertures plus the on-axis
one. The off-axis apertures are provided by two illumination rings incoming from two different
values of the prism's deviation angle. (
y) are the width and height, respectively, of the CCD
elementary aperture.
Δ
x,
Δ
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