Speedy Light Slowed to a Crawl in Liquid Crystal Matrix

Light speeds through space, bouncing off objects as it races at about 186,282 miles per second. Now, scientists may have found a way to halt this mad dash. They've discovered that they can slow light by using embedded dye molecules in a liquid crystal matrix; the findings could one day lead to new technologies in remote sensing and measurement science.

Scientists have long known that a wave packet of light becomes more sluggish when it travels through matter. Yet the magnitude of this slow-down in typical materials such as glass or water is less than a factor of two. That's why researchers decided to see if there was another way to slow down light a bit further.

The new approach to manipulating light involves taking advantage of the fact that when light travels as a pulse, it is really a collection of waves, each having a slightly different frequency. All waves in the pulse must travel together, which means that scientists can design materials to be like obstacles courses that "trip up" some of the waves more than others. In order to exit the material together, the pulse must wait until it can reconstitute itself.

In this case, the researchers used a liquid crystal similar to the materials used in LCD television and computer displays that could operate in a simple setup, does not require external voltages or magnetic fields and works at room temperature. The scientists then added a chemical component that twisted the liquid crystal molecules into a helical shape and then added dye molecules that rested in the helical structures. The dye molecules change their shape when irradiated with light, thus altering the optical properties of the material.

So what can this light do? If scientists can slow down the light enough, they could potentially store the pulses for optical communications. While the long length of the light pulses in this study makes this application impractical, the technique is well suited to sensing and interferometry applications. In fact, it can be potentially be used to build a highly sensitive instrument that works on a principle similar to the concept behind a police officer's radar gun.

"Realizing slow and stopped light in these media is very exciting both for the fundamental research that discovers such new effects in soft matter systems, and for the new possibilities that these investigations could open in the fields of remote sensing and optical storage, said Umberto Bortolozzo, one of the researchers, in a news release.

The findings are published in two papers, one in Optics Express and one in Optics Letters.