Inspire Two Laser Designs
The structure in feathers that gives bluebirds (among other animals)
such brilliant color inspired researchers at Yale University, U.S.A., to copy
the pattern to create lasers. At OSA’s
Frontiers in Optics meeting last year,
Hui Cao of Yale described the lasers
in his presentation,“Bio-inspired photonic nanostructures and lasers” (paper
FW W1, 2011).
An animal’s color does not come from
pigment, but from reflective nanostructures. Unlike di;raction gratings, however, the structures appear disordered
and reflect the same color from many
angles. ;e materials don’t contain large-area order, but there is some short-range
order that scatters light preferentially
at specific wavelengths. Based on those
natural structures, Cao and her group at
Yale created two lasers that use short-range order to control light.
In May, Heeso Noh and colleagues in
Cao’s group reported building a laser by
recreating the structure of bird feathers
(Phys. Rev. Lett.
106, 183901). Tiny
spheres of air embedded in the feathers’
proteins reflect light at
;e group etched
an array of roughly
into a gallium arsenide film. Indium
arsenide quantum dots were used as a
gain medium. When optically pumped,
the film lased with wavelengths that
depended on the size of the holes and
the distance between them.
Researchers also found a second
structure in the feathers: a series of
twisty interconnecting nanochannels.
Like the spheres, their structure also
appears random in the larger scale, with
only short-range order. ;e “network”
laser based on this design blocks certain
colors of light while allowing others
to propagate (Opt. Lett. 36, 3560). In
The nanostructures that give
bird feathers their brilliant colors
inspired the design of lasers that
may someday self-assemble.
both cases, the lasers’ colors depend on
the width of the nanochannels or the
spacing between the nanoholes. ;e
network laser works better, Cao says. “It
outperformed the first one because the
photonic bandgap can be formed now
without long range order.”
Building lasers without mirrors and
the strict requirements for long-range
order of photonic crystals could make it
easier to fabricate lasers—and possibly to
use self-assembly methods that have been
used in the production of color-producing
nanostructures in bird feathers.
Imaging on a Cellphone?
There’s an App for That
A group of California scientists has developed small, inexpensive
attachments that allow high-definition
cellphone cameras to perform microscopy and spectroscopy in the visible
region. Although the resolution of the
device is not as good as dedicated commercial equipment, it is good enough
to distinguish between healthy and
diseased blood samples and to detect
fluorescent dyes, according to Sebastian
Wachsmann-Hogiu of the University
of California Davis Medical Center’s
Center for Biophotonics, U.S.A.
;e Davis team is one of several research groups leveraging
recent advances in cellphone camera
technology to make low-cost imaging
applications for medical care in the
developing world. Davis postdoctoral
fellow Kaiqin Chu presented her group’s
work at the Frontiers in Optics meeting in San Jose, Calif., U.S.A. (paper
;e microscopy attachment consists
of a 1-mm ball lens mounted in a rubber
aperture to exclude light from outside
the region of interest. Unlike comparison
images from a commercial microscope,
the cellphone images have edge distortions because the detector is relatively
large compared to the lens.
Z.J. Smith et al.
An iPhone microscope, which consists
of a 1-mm-diameter ball lens embedded
in a rubber sheet and taped over the
Still, the cellphone microscope
achieved 1.5-µm resolution (most
modern phones have pixels 1 to 2 µm
in size)—not as fine as 0.5 µm on a
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