Better Detection of
S. Nakagomi, Ishinomaki
Researchers at Ishinomaki Senshu University (Japan) have devised a
photodiode for rapid detection of short-wavelength UV light (Appl. Phys. Lett.
103, 072105). The technology could help
monitor levels of atmospheric ozone,
make better flame sensors and improve
Ultraviolet photons in the UVC band
with wavelengths from 280 nm down
to 100 nm can break bonds within DNA
molecules, which give them germicidal
properties against microorganisms.
However, they can also harm skin and
eyes and create ozone from oxygen molecules. Shinji Nakagomi and colleagues
created the photodiode out of two
semiconductors, n-type gallium oxide
and p-type silicon carbide. Together, they
form a heterojunction (p–n) between
semiconductors with different band gaps.
Previous attempts at making solid-state UVC detectors used aluminum
nitride and diamond with band gaps of
6. 3 and 5. 47 eV, respectively—too large
to detect radiation through the entire
UVC region. Gallium oxide, on the other
hand, has a band gap of 4. 9 eV, which
picks up all UVC rays while remaining
“solar blind” to longer wavelengths.
Crystal model of
b-Ga2O3. Imaging Breast Cancer with Light
Routine screening can increase breast cancer survival by detecting the disease early and allowing
doctors to address it at this critical
stage. Researchers at the University of
Twente (Netherlands) have developed a
prototype that may one day help to detect
breast cancer when it’s most treatable
(Biomed Opt. Exp. 4, 2555).
In the new imaging technique,
infrared light is delivered in billionth-of-a-second pulses to tissue, where
it is scattered and absorbed. The high
absorption of blood causes a slight
increase in blood vessel temperature,
which causes the vessels to slightly and
quickly expand. This expansion generates
ultrasound waves that are used to form a
3-D map of the breast vasculature. Since
cancer tumors have more blood vessels
than the surrounding tissue, they are
distinguishable in this image.
If effective, the new “photoacoustic
mammoscope” would represent an
entirely new way of imaging the breast
and detecting cancer. —Sarah Michaud
An XY plane image slice at 40 mm depth
from the model surface. Visualized objects
include an object that mimics a blood
vessel ( 1) and an object that mimics a
tumor ( 5).
Biomed. Opt. Express