T-Ray filter: Terahertz radiation causes waves to propagate through electrons in a metal sheet. Where the waves bend around holes in the sheet, the resulting electric field causes the emission of terahertz radiation at a single frequency. That could allow different frequencies to be encoded with different information, increasing capacity in a wireless network. Credit: Bryan Christie

Photons--particles of light--are good at carrying energy and information through space; electrons aren't, but they're easier to control. Many modern technolo­gies--imaging systems, solar cells, information networks--need to mediate between footloose photons and well-behaved electrons, but getting the particles to interact with each other can be a challenge.

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