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A Practical T-Ray Amplifier

Terahertz sensors can see through clothing and sniff for bombs, but they've had to do so with very weak signals

3 min read

2 December 2009—Terahertz time-domain spectroscopy is a tantalizing technique for scientists wanting to characterize materials and for those charged with securing airports and other sensitive locations. Unlike X-rays, terahertz radiation—which lies above microwave wavelengths and below the infrared band, in the 30 micrometer to 1 millimeter range—doesn’t damage biological tissue and provides good resolution. Many molecules—including those in explosives and narcotics—have spectral signatures that lie in the terahertz range. And terahertz radiation is absorbed by water, so it can be used to determine a material’s water content.

Yet “terahertz technology is extremely underdeveloped compared with other portions of the electromagnetic energy spectrum,” says Nathan Jukam of the Pierre Aigrain Laboratory at the École Normale Supérieure, in Paris. Terahertz radiation, which is generated by ultrashort-duration lasers, is often weak, and it is difficult to amplify the terahertz signal without using large, complex, and costly laser systems.

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The Transistor at 75

The past, present, and future of the modern world’s most important invention

2 min read
A photo of a birthday cake with 75 written on it.
Lisa Sheehan

Seventy-five years is a long time. It’s so long that most of us don’t remember a time before the transistor, and long enough for many engineers to have devoted entire careers to its use and development. In honor of this most important of technological achievements, this issue’s package of articles explores the transistor’s historical journey and potential future.

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