One of the most rapidly developing fields in science and technology is
photonics; i.e, using light (photons) to process information in a manner
analogous to electronics. Photonics has played a major role in advances
in the telecommunications industry such as fiber optics. Futhermore, the
next generation of supercomputers will be all-optical. The tremendous interest
in this field has created a demand for high tech materials that have the
necessary properties for applications. Organic and polymeric materials have
shown great promise in this area because of their wide-ranging properties.
Many of the materials used for photonics are non-linear optical (NLO) materials,
which means that they interact with light in such a way that the light changes
the properties of the material, which, in turn, changes the properties of
the light. This can give rise to a number of interesting effects such as
frequency conversion, in which light of one color (frequency), is transformed
into light of a different color upon passing through the NLO material, for
example, red light can be converted into green. NLO materials are used for
making photonic devices such as optical switches, optical memories, and
logic gates. Organic and polymeric materials can have very large and very
fast (on the order of 10-15 seconds) NLO
responses, which is critical for applications in many devices. At Marshall
Space Flight Center's Space Sciences Laboratory, we have been studying two
important classes of organic NLO materials: phthalocyanins, which are large
ring-structured molecules, and polydiacetylenes, which are long zig-zag
polymers. The picture below shows the Phthalocyanin ring structure (on the
left) and the Polydiacetylene repeat unit (at right).
In order to take advantage
of their properties, NLO materials must be processed into useful forms,
generally crystals or thin films. In order to have high performance, these
crystals and films must be very pure, free of defects, highly uniform, and
have proper molecular orientation. On Earth, the formation of such crystals
and films is hindered by gravity, which gives rise to effects such as natural
convection and sedimentation. These effects can cause undesirable mixing,
fluid flows, and settling during processing that can reduce the quality
of the NLO materials obtained.
In the low gravity enviroment of space we can escape these negative effects
and study the processing of NLO materials under more ideal conditions. Thin
films of both phthalocyanins (3M Corporation - Physical Vapor Transport
of Organic Solids, 1985) and polydiacetylenes (Marshall/University of Alabama
at Huntsville - Polymer Thin Film Growth, 1995) have been grown aboard the
Space Shuttle.
The upper picture at left shows copper Phthalocyanin films (at 30,000X magnification)
grown in space. The lower picture shows the same films grown on Earth. Note
the improvement in molecular order and packing in the space-grown film.
The images
on the right show Polydiacetylene films (500X) grown on Earth (on left),
and in space (at right). Note the reduction in the number of defects (dark
spots) in the space-grown film.
The knowledge gained from these studies will help us to better understand
how crystals and thin films of organic and polymeric NLO materials are formed,
from which processing conditions on Earth can be optimized. In the future,
production of NLO materials may actually be carried out in space aboard
the Space Station, yielding materials with superior properties to those
possible on Earth.
For further information on Non-Linear Optical materials, contact
Dr. Mark S. Paley or Dr. Donald O. Frazier
Space Sciences Laboratory/ES71
Marshall Space Flight Center
Huntsville, AL 35812
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Headlinesreturn to Space Sciences Laboratory Home
Author: Mark S.
Paley
Curator: Bryan Walls
NASA Official: John M. Horack