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Terahertz Center Opening Signals Wave of RPI's Future

Photonics.com
Dec 2003
TROY, N.Y., Dec. 10 -- Change is in the air at the Rensselaer Polytechnic Institute (RPI).

Bulldozers were poised at a campus construction site last Friday -- a cloudy, bitingly cold day that foreshadowed what would become a record-breaking snowstorm over the weekend.

An RPI staff member voiced her anxiety about the fate of the NCAA Division III Football Championship Regional Final scheduled for Saturday; the team went on to play in blizzard-like conditions and "held off Ithaca College 21-16, advancing to its first-ever appearance in the NCAA National Semi-Finals," said an article on the RPI Web site. It featured a photo of a triumphant, parka-clad Shirley Jackson, RPI's 18th president, with the caption, "We Won!"

The bulldozers and Jackson's victorious attitude are two indicators of what's ahead for RPI, dubbed a "renaissance" since she came on board in 1999.

The ongoing construction is for a number of development projects, two of which are a Biotechnology and Interdisciplinary Studies Research Center -- a mix of laboratories, laboratory support space, offices and seminar facility; and an Experimental Media and Performing Arts Center, which will house a theater, recital hall, a series of "black box" theaters and dance/music recital space, among other things.

RPI also recently remodeled its nanotechnology research center (also know as the National Science Foundation Center for Directed Assembly of Nanostructures); in September, the school opened an office in Washington, D.C., that Jackson said will be "a platform to participate more directly and more consistently in the decision-making process that affects research universities and their roles in the technological research community."

Inside, amid the 19th-century brick buildings that form the core of the Troy campus, there's even more evidence of progress. And the intangible terahertz wave will be a tangible part of it.

On that cold Friday, on the ninth floor of the Low Center, Jackson presided over the dedication of the W.M. Keck Laboratory for Terahertz Science, part of RPI's new Center for Terahertz Research.

The next frontier
"Under the leadership of Xi-Cheng Zhang, the terahertz research team at Rensselaer has become the world leader in the development and application of terahertz technology," said Jackson to a standing-room-only audience attending the dedication. "The support of the W.M. Keck Foundation will now allow the Rensselaer team to do what no other research group has done before: to create and detect terahertz waves at extreme levels, in the nonlinear range. The potential gains to be made by this research will form the next frontier in scientific discovery."


RPI's new W.M. Keck Laboratory for Terahertz Science, part of the Center for Terahertz Research (Photo: Kris Qua, courtesy RPI)
Her perspective is not only that of a highly paid administrator and fund raiser; Jackson has a PhD in theoretical elementary particle physics and an SB in physics from the Massachusetts Institute of Technology; she is also a former chairman of the US Nuclear Regulatory Commission and has worked as a theoretical physicist at the former AT&T Bell Laboratories and as a professor of theoretical physics at Rutgers University.


RPI President Shirley Jackson at the dedication of the Keck lab.
Scientists are drawn to this elusive portion of the electromagnetic spectrum, which lies between infrared and microwave bands, because of the advantages that terahertz waves, or "T-rays," offer over conventional imaging technologies. Unlike x-rays, T-rays can be focused and are capable of producing images with signature or fingerprint capability, also called functional imaging. T-rays' low-photon energy levels allow the imaging of biological tissue without harmful ionizing radiation, making them safer than x-rays. And the unique vibrational, rotational and translational responses of materials within the THz range provide information generally absent in optical, x-ray and nuclear magnetic resonance (NMR) images, enabling a sort of THz wave fingerprint of the molecular structure of the material being imaged. This fingerprinting will allow T-rays to one day be used to detect harmful biological or chemical agents.

Terahertz waves have the potential to create pictures and transmit information in the same way that visible light can create a photograph, radio waves can transmit sound and x-rays can "see" shapes within the human body. But T-rays paint a picture in more intricate detail, and pose few safety risks to biological tissue, making the technology beneficial to many aspects of biomedicine and for earlier detection of disease.

Terahertz sensing and imaging systems that see through walls have the potential to examine and identify asbestos or radiation contamination, search for landmines or plastic explosives, or help police locate hostages, terrorists and weapons during a standoff. Terahertz-based tools will be valuable in many other fields, including biomedical imaging, agriculture, forensic science and food safety, RPI said.


THZ TEAM LEADER: Xi-Cheng Zhang (seated) is the J. Erik Jonsson '22 Distinguished Professor of Science and founding director of the Center for Terahertz Research. Rensselaer is investing heavily in the center, providing 5,000 square feet of laboratory space for a new THz laboratory in the Low Center for Industrial Innovation, as well as substantial money for renovation and equipment. Standing: doctoral student Shaohong Wang. (Photo: Mark McCarty, courtesy RPI)

Scientists also expect that terahertz science will have a profound impact on biotechnology, where T-ray spectroscopy of biological molecules could provide new tools to study protein folding or a monolayer of DNA. For example, the Rensselaer team has successfully characterized the process by which a protein changes its shape when subjected to chemical or physical forces such as heat, and protein-protein interaction at terahertz frequency.

Out of hiding
Although THz radiation always has been part of the electromagnetic spectrum, it received little attention until the early 1990s, according to RPI's alumni magazine, Rensselaer (March 2003).

"THz radiation, which ranges from 100 gigahertz to 10 terahertz, is but one type of the radiation, or waves of energy, that fills the world around us," the article said. "Radio waves, the lowest frequencies, carry sound through space. Moving up the spectrum to higher frequencies, the electronic waves are found that carry messages on computer chips and the microwaves that rapidly cook food. Higher still are visible rays (light), x-rays and others."

While many of these radiation frequencies have been extremely useful, there has been no technology available to exploit the large band that lies between microwaves and visible light-far infrared, or THz, radiation, according to the article, but that changed about 10 years ago.

Well-equipped

The new Keck Laboratory is supported by a $1 million W. M. Keck Foundation grant and substantial money from RPI for renovation and equipment. The 5000 square-foot "world-class lab" is equipped with advanced instrumentation including a three-phase terawatt system, which uses an amplified laser pulse to produce a high-powered terahertz wave. The lab is also outfitted with an infrared spectrometer, optical tables and a vacuum deposition system.

The center's four labs are equipped with the most advanced photonic and opto-electronic instrumentation for generating, measuring and recording picosecond and femtosecond terahertz radiation waves. The research center currently supports four faculty members and at least 30 graduate and 30 undergraduate students.

In October, RPI was awarded a $3.86 million grant from the National Science Foundation (NSF) to fund 15 fellowships to enhance interdisciplinary graduate study in terahertz science and technology as it relates to imaging, data transfer and networking systems and electronics.

"Terahertz research is one of the most intriguing and challenging fields to emerge in the 21st century," said Gwo-Ching Wang, professor and chair of the Department of Physics, Applied Physics and Astronomy, who worked with more than a dozen faculty to secure the NSF grant. "In less than a decade, this previously hidden section of the electromagnetic spectrum has caught the imagination of scientists around the world."


©The Center for Science Education at UC Berkeley (Illustration: Bina Butt, Ideum)


T-ray pioneers
Rensselaer faculty are among the world's first scientists to exploit the unique advantages of THz radiation. Zhang is one of the leaders in the research that has made THz technology possible. He has developed both emitters to send out THz radiation and detectors to pick up the radiation so information can be obtained from it. His Rensselaer research group has explored the uses of T-rays for imaging and for obtaining spectroscopic information about items that range from dollar bills to breast cancer phantoms.

In addition to Zhang, the center has three other faculty members: Michael Shur, the Patricia W. and C. Sheldon Roberts'48 Professor of Solid State Electronics at Rensselaer; Roland Kersting, assistant professor of physics and a member of Rensselaer's information technology faculty; and assistant professor Ingrid Wilke.

The promise of terahertz wave radiation is being realized through ongoing research at the THz center's four state-of-the-art laboratories: Zhang's THz optoelectronics lab, Shur's THz electronics lab, Kersting's THz quantum optics lab and Wilke's THz spectroscopy lab. Together, these researchers are overcoming significant challenges posed by the lack of understanding of the fundamental physics that underlie this large portion of the electromagnetic spectrum.

Shur brings to the THz center his fundamentally new concept of superfast plasma-wave signals on solid-state devices. (He is also director of Rensselaer's new IBM Center for Broadband Data Transport Science and Technology.)

Closing the 'terahertz gap'
Shur and Kersting are among the first scientists in the world to create prototype devices for systems that use terahertz waves to carry microelectric signals. Their pioneering research with terahertz-speed electronic devices has been credited with closing the "terahertz gap" -- the term for the scientifically rich but technologically undeveloped THz frequency. Wilke pioneered the application of single-shot THz-radiation pulse measurements to femtosecond relativistic electron beam bunch length measurements. This is a significant advancement of electron beam diagnostics for new types of x-ray free electron laser and high-energy physics, RPI said.


Center for Terahertz Research faculty (left to right) Michael Shur, professor of solid state electronics; Roland Kersting, assistant professor of physics and a member of Rensselaer's information technology faculty; and assistant professor Ingrid Wilke (Photos: Mark McCarty [left and center], Gary Gold; courtesy RPI)
RPI's THz research faculty's breakthroughs in developing electro-optic THz emitters and detectors have opened the door to sensing and imaging opportunities for academic and industrial applications and earned them six patents, with another several pending.

The sensing techniques developed by Zhang and his research team are now being used worldwide. The research team is one of the few groups in the world that is successfully building demonstration prototypes of terahertz-speed electronic devices. More than 100 research groups around the world use terahertz sensing in physics, electrical engineering, material science and chemistry. More than 350 scientists and engineers from government and industry laboratories, universities, clinics and medical schools have visited Zhang's labs, and he has helped scientists from 17 countries learn to use these electro-optic terahertz sensors, the university said.

Uncovering defects
Researchers at Rensselaer have also used advanced THz technology to uncover small defects in the foam used for space shuttle insulation.

Research at the center is currently focused on the generation and detection of free-space THz beams using ultrafast optics and electro-optic crystals. A primary goal is to develop and refine the instrumentation -- finding higher dynamic ranges, achieving faster data acquisition, and increasing sensitivities to enable the detection of monomolecular layers -- that will move THz technology beyond its current niche applications to support wider use in biomedicine.

Perhaps the greatest potential for this research lies in biomedical imaging and genetic diagnostics. T-rays offer hope for improved detection of breast cancer through sharper imaging and molecular fingerprinting. Each year, more than a half million biopsies of breast tissue are required to compensate for inaccurate and uncertain diagnoses using current detection methods. Zhang has begun working with doctors at the Boston Medical Center, using THz systems developed at Rensselaer to identify breast tumors. Another medical research team in England has received a grant of $6 million to perform clinical studies using the technology developed here. Nikon in Japan has developed a commercial T-ray imaging system based on Rensselaer's invention.

Rensselaer's terahertz research group has received nearly $10 million in grants from the National Science Foundation, Army Research Office, Army Research Laboratory, Air Force Office of Scientific Research, Defense Advanced Research Projects Agency, Department of Energy, Research Corp., IMRA America Incorporated, Molecular OptoElectronic Corp. and Zomega Technology Corp.

"Working together, the investigators at the Center for Terahertz Research have made remarkable accomplishments," said Dean of Science Joseph Flaherty. "We hope to recruit additional faculty in terahertz science to expand the center's range and influence and secure our leadership position."

For more information, visit: www.rpi.edu/terahertz



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