You’ve probably never heard of terahertz waves, but they could change your life

 From PopSci.com (Mar. 22, 2022):

There’s a gap on the electromagnetic spectrum where engineers can not tread.

The spectrum covers everything from radio waves and microwaves, to the light that reaches our eyes, to X-rays and gamma rays. And humans have mastered the art of sending and receiving almost all of them.

There is an exception, however. Between the beams of visible light and the blips of radio static, there lies a dead zone where our technology isn’t effective. It’s called the terahertz gap. For decades now, no one’s succeeded in building a consumer device that can transmit terahertz waves.

“There’s a laundry list of potential applications,” says Qing Hu, an electrical engineer at MIT.

But some researchers are slowly making progress. If they stick the landing, they might open up a whole new suite of technologies, like the successor to Wi-Fi or a smarter detection system for skin cancer.

The mystery of the terahertz

Look at the terahertz gap as a borderland. On the left side, there are microwaves and longer radio waves. On the right side lies the infrared spectrum. (Some scientists even call the terahertz gap “far infrared.”) Our eyes can’t see infrared, but as far as our technologies are concerned, it’s just like light.

Radio waves are crucial for communication, especially between electronic devices, making them universal in today’s electronics. Light powers the optical fibers that underpin the internet. These realms of technology typically feed off different wavelengths, and uneasily coexist in the modern world.

But both realms struggle to go far into the terahertz neutral zone. Standard electronic components, like silicon chips, can’t go about their business quickly enough to make terahertz waves. Light-producing technologies like lasers, which are right at home in infrared, don’t work with terahertz waves either. Even worse, terahertz waves don’t last long in the Earth’s atmosphere: Water vapor in the air tends to absorb them after only a few dozen feet.

There are a few terahertz wavelengths that can squeeze through the water vapor. Astronomers have built telescopes that capture those bands, which are especially good for seeing interstellar dust. For best use, those telescopes need to be stationed in the planet’s highest and driest places, like Chile’s Atacama Desert, or outside the atmosphere altogether in space.

The rest of the terahertz gap is shrouded in mist. Researchers like Hu are trying to fix this, but it isn’t easy. [read more]