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Bridging the terahertz gap

By Jay Rizoli

Originally appeared in Mass High Tech, July 21, 2003

The 19th-century building at 20 Birge St. in Brattleboro was once the source of sounds that would ultimately be heard all over the world.

As part of the industrial complex that housed the Estey Organ Co. from 1869 to 1959, the clapboard structure was one component of a company that produced more than 500,000 reed organs — some of which are still in use — for homes and churches worldwide.

Today the vibrations coming from inside the building are of a distinctly different sort, but the impact of the technology developing there may be monumental nonetheless.

The former Estey building, looking much as it might have when Jacob Estey and Co. moved in, is the home of Vermont Photonics, supplier of optical test equipment and optical metrology equipment and developer of tunable terahertz technology.

And if you’ve never heard of terahertz, that’s because it’s been hiding. Terahertz — “the final frontier of the electromagnetic spectrum,” the company calls it — is the part of the electromagnetic spectrum that falls between the infrared and the microwave (see graphic below); a terahertz is equal to 1 trillion hertz, and terahertz radiation holds promise in biotechnology and nanotechnology and for scientists studying chemistry, phonons, polymers, water, biophysics, superconductors, semiconductors and drug discovery.

“We are on the threshold of an exploding field and in a very good position,” says Vermont Photonics co-founder and managing director Mike Mross of the company’s tunable terahertz laser source. “In our opinion it’s the most useful technology in the terahertz area.”

Vermont Photonics’ tunable terahertz source produces narrow-band terahertz that is tunable over a broad range. The “terahertz gap,” in the output range of 100 to 1,000 microns, is the domain of Vermont Photonics’ Smith-Purcell THz device. The compact terahertz device is a means to drive proteins and other nanostructures at their inherent resonances — the unique way that molecular structures respond to a certain stimulus, like the frequency of a ringing bell — to produce “terahertz fingerprinting.”

Mross’s pursuit of terahertz evolved from the work of his Dartmouth College professor John E. Walsh, whose method of producing terahertz grew from plasma beam radiation research.

“In the early ’80s it occurred to me that for the infrared part of the spectrum it could be invaluable,” said Mross, a plasma physicist. “It was a part of the spectrum that people had no idea how this responded to these frequencies.”

So with an exclusive agreement with Dartmouth to use the technology, Mross and former colleague Tom Lowell founded Vermont Photonics in 1985. The four-person company is a distributor of visual and electronic autocollimators for Wedel, Germany-based Möller-Wedel Optical GmbH, selling state-of-the-art equipment to other companies for the quality control of optical equipment and precisely measuring very small angles.

“So we’re an engineering consultant company; we offer the equipment and show how to apply it,” Lowell said. “And we’re very proud that we have some very loyal customers over the years,” among them Boeing, Eastman Kodak, Los Alamos National Labs, Northrop-Grumman, Raytheon and Rockwell International

But their R&D is devoted to the tunable terahertz laser.

“People say, ‘Why do you want to be in that part of the spectrum? Nobody does anything there,’ ” Mross says, to which Lowell counters, “That’s why we want to be there.”

Mross cites the invention of the klystron tube, a high-frequency amplifier for generating microwaves that revolutionized high-energy physics and microwave.

“The people who invented the klystron didn’t know it would end up in all those microwaves, so we’ve been doing whatever we can to get in on the ground floor. We know there will be lots of things you can do in that (terahertz) gap.”

Those may include developing new materials, unfolding the corrupted proteins of bovine spongiform encephalopathy (“mad cow” disease) or even battling bioterrorism.

“The world is becoming concerned about biological agents, and it’s possible to use terahertz to identify materials,” Lowell said. “So there’s interest from DARPA in using terahertz for the identification of biochemical agents.”

Such concepts are what have driven Vermont Photonics for close to 20 years.

“We’re not aimed at a product,” Lowell says. “We’re aimed at intellectual property.