corrosive bleach solution for three months
and found no decrease in performance.
Pan said the team will continue to tune
the compositions and processing condi-
tions to find materials that are more sensi-
tive to visible sunlight activation. They
also plan to explore the applications of
the materials in high-efficiency silicon
solar cells and deep-tissue bioimaging.
Lastly, they will expand the material
systems to discover other series of NIR
A cartoon featuring five monkeys was drawn with paint that was made by mixing NIR persistent powder
into a water-based indoor wall paint. Courtesy of Grace Pan and Zhengwei Pan.
Optical resonator builds better UV beam
ANN ARBOR, Mich. – An optimized optical resonator can be a better way to build
compact ultraviolet light sources with low
power consumption, which could lead to improved data storage and chemical analysis.
Researchers at the University of Michigan optimized a whispering gallery resonator to take an infrared signal from
relatively cheap telecommunications-compatible lasers, using a low-power nonlinear process to boost it to a higher-energy UV beam. The optical resonator is a
millimeter-scale disk with a precisely engineered shape and smooth surface polishing to encourage the input beam to gain
power as it circulates inside, allowing researchers to make low-cost, wavelength-tunable UV sources using low-infrared
The researchers used their resonator to
generate the fourth harmonic of the infrared beam with which they started.
“We experimentally demonstrate, for
the first time, continuous-wave cascaded
harmonic generation up to the fourth-har-monic in a lithium niobate whispering
gallery resonator – which allows us to
convert a telecommunications-compatible
infrared light beam to an ultraviolet light
beam at pump power levels as low as
200 mW,” said Mona Jarrahi, an assistant
professor in the department of electrical
engineering and computer science at the
By pushing light beams through a nonlinear medium, they can coax out offshoot
beams that are double – or, in this case,
quadruple – the frequency and energy of