A new gatekeeper for light discovered

Imagine a device that is selectively transparent to various wavelengths of light at one moment and opaque to them the next, following a tiny adjustment.

Now, researchers from University at Buffalo's (UB) school of engineering and applied sciences reported a discovery that brings us one step closer to this.

Such a gatekeeper would enable powerful and unique capabilities in a wide range of electronic, optical and other applications, including those that rely on transistors or other components that switch on and off.

The finding has to do with materials that are periodic which means that they are made up of parts or units that repeat.

Crystals fall into this category as do certain parts of the wings of butterflies, whose periodic structure helps give them color by reflecting specific colours of light.

Scientists have known since the early 20th century that periodic materials have special qualities when it comes to light.

Such materials can reflect light as butterfly wings do and if you understand the internal structure of a periodic material, you can use an equation called Bragg's law to determine which wavelengths will pass through the material, and which will be blocked due to reflection.

The new study showed that a completely periodic material structure is not needed for this kind of predictable reflection to take place.

"We have shown that Bragg's law is a special case of a more generalised phenomenon that was discovered in this study and named as a Bloch wave resonance," said Victor A Pogrebnyak, adjunct associate professor of electrical engineering at UB.

This discovery opens up new opportunities in photonics, nanoelectronics, optics and acoustics and many other areas of science and technology that exploit band gap wave phenomena for practical use.

The Bloch wave resonance enables the blocking of a larger range of wavelengths simultaneously than previously known effects described by Bragg's law.

Applications that could take advantage of this broader "band gap" range include white light lasers and a new type of fast-switching transistor.

The research appeared in the journal Physical Review Letters.

--IANS

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