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Lighthouses use Fresnel lenses, developed in the
19th century, to allow ships to navigate safely in
coastal waters and serve mankind ever since.
21 Laser Focus World www.laserfocusworld.com September 2013
unsuitable to give highly quantitative measurements, but very
good at giving present/not-present detection at very high sen-sitivities). Combining the two different sensor technologies into
one system would enable new applications, he notes.
“We believe that overall there is great potential for a new
field of plastic-based integrated optical components that go far
beyond the current demonstrator,” he says. “We are working
on many such devices, including plastic-based lasers, light
sources, sensors, and optical interconnects.” —John Wallace
REFERENCE
1. S. Z. Oo et al., Opt. Exp., 21, 15 (July 29, 2013).
CONFOCAL MICROSCOPY
Dual-detection confocal
fluorescence microscope
needs no axial scanning
One of the most effective ways to observe living tissue is by
using a confocal fluorescence microscope, which allows detailed
3D fluorescence information to be captured and used to reconstruct 3D images. However, because a confocal microscope
must normally be scanned in three dimensions, biological
samples can be photobleached, damaged, or even killed by the
large amount of light received.
Four researchers at the Korea Advanced Institute of Science
and Technology (KAIST; Daejeon) and Hanyang University
(Seoul) have greatly lessened the problem of light toxicity in
confocal fluorescence microscopy by creating an instrument that
only needs to be scanned in two dimensions (x and y) rather than
in all three (axial, x, and y). The researchers, who include Dong-Ryoung Lee, Young-Duk Kim, Dae-Gab Gweon, and Hongki Yoo,
achieve this by using two pinhole-covered photodetectors, each
pinhole of a different size and thus a different axial response.
Axial information from emitting points is obtained by looking at
the ratio of intensity signals from the pinholes and using their
axial response to place the depths of the points.
In the technique, called dual-detection confocal fluorescence
microscopy (DDCFM), the two pinholes are a fixed axial distance
apart. The ratio of the signals from the two detectors is the
relevant measured parameter; thus, characteristics such as a fluorescent sample’s quantum efficiency drop out of the calculations
and a simple response curve results.
180 µm depth range
The experimental system was based on pinhole diameters of 30
and 150 µm; a 488-nm-emitting laser was the light source. Two-dimensional scanning was done with a galvanometer mirror and
an 8 kHz resonant mirror, resulting in 15. 6 frames/s, each frame
with 512 × 512 pixels. The field of view was 4000 × 4000 µm.
