Growing Computers in Space?

 

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