The researchers have succeeded in taking semiconducting polymers �
plastics that consist of long chains of atoms that work as
semiconductors - and stretching them out in a
silica (glass) host matrix so that they have new optical properties.
�If you have polymer chains that can wiggle like spaghetti, it�s hard
to make them all point in the same direction,� Tolbert said. �What we
do is take tiny, nanometer-sized holes in a piece of glass and force
the polymer chains into the holes. The holes are so small that the
spaghetti chains have no space to coil up. They have to lie straight,
and all the chains end up pointing in the same direction.�
Because the chains point in the same direction, they absorb polarized
light and give off polarized light. Lining up the polymer chains also
provides advantages for laser technology, because all the chains can
participate in the lasing process, and they can make the light
polarized without the need for any external optical elements, Tolbert
said.
As a postdoctoral fellow, Schwartz was one of the original discoverers
in the 1990s that lasers could be made out of randomly oriented
semiconducting polymer chains.
�Our new materials exploit the fact that the polymer chains are all
lined up to make them into lasers that function very differently from
lasers made out of random polymers,� Schwartz said.
The manner in which the polymer chains incorporate into the porous
glass of the silica matrix helps to confine the light in the material,
enhancing the lasing process by producing what is known as a
�graded-index waveguide.� In most lasers, confining the light is
typically done with external mirrors.
�Our materials don�t need mirrors to function as lasers, because the
material that�s lasing is also serving to confine the light,� Schwartz
said.
In combination, the alignment of the polymer chains and the
confinement of the light make it 20 times easier for the new materials
to lase than if a randomly oriented polymer sample were used. And
because polymers can be dissolved easily in solvents, they are
inexpensive to process. The glass host matrix with the aligned
nanoscale pores is also inexpensive to produce.
�Usually polarized and cheap don�t go together,� Tolbert said.
The research opens the possibility of additional applications for the
new materials as a brighter polarized source for displays in products
with LED-type displays, including cell phones, laptops and Palm Pilots.
�If you take an inexpensive light source with which you could excite
the aligned polymer chains and get the chains to reemit, you
potentially have a more efficient way to generate polarized light.�
Tolbert said. �This would allow displays to be brighter with less
power consumption, and you could get longer battery life.�
Tolbert has collaborated with Canon for years on the development of
this class of new materials.
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