OSU researcher lights the way of the future

Wednesday, August 29, 2007

OSU Regents Professor and Bellmon Professor of optoelectronics Daniel Grischkowsky was on the team of IBM scientists that in 1986 broke the "picosecond barrier" by combining a laser and an electronic switch to produce electrical pulses that lasted one trillionth of a second. His growing recognition as a pioneer of terahertz science has coincided with its advancement this century as a field of optics and photonics. While maintaining a productive, world-class research program at OSU, Grischkowsky is invited frequently to address international conferences and has appeared as a guest of honor at the dedications of new terahertz research facilities, including the W.M. Keck Laboratory at Rensselaer Polytechnic Institute.

Digital devices capable of transmitting in one second enough data to fill an encyclopedia set and medical imaging more revealing and safer than X-rays are some of the innovations that may become possible due to Daniel Grischkowsky’s contributions to the science of light. The world will need a few years to appreciate his impact, but the scientific community already has ranked Grischkowsky, Regents Professor and Bellmon Professor of optoelectronics at Oklahoma State University, among the most influential optical engineers and scientists of the 20th century.

A paper by Grischkowsky is one of the Journal of the Optical Society of America’s top 50 articles most cited by other academicians, scientists, engineers and researchers. Based on a tally of the citation index of the Institute for Scientific Information (ISI) Web of Science, the articles were compiled and reprinted online by the society in celebration of 90 years of publishing peer-reviewed, scientific journals.

Included are seminal works by three-dimensional holography inventor Emmett Leith, Jones calculus creator and namesake R.C. Jones and renowned inventor Edwin Land, whose polarizing films spawned the Polaroid Corporation and its instant camera.

Cited 378 times since its 1990 publication, “Far-Infrared Time-Domain Spectroscopy with TeraHz Beams of Dielectrics and Semiconductors” documented a study on electromagnetic waves at terahertz frequencies by Grischkowsky and his post-doctoral colleagues Soeren Keiding, Martin van Exter and Ch. Fattinger at IBM’s Watson Research Center.

The groundbreaking project, an analysis of the interaction between terahertz radiation and materials designed to conduct as well as insulate against electromagnetic waves, introduced techniques that became the basis for terahertz time-domain spectrometers in use worldwide today.

It was also a preview of the work Grischkowsky has done at OSU since he left IBM in 1993 to become a member of the College of Engineering, Architecture and Technology faculty.

“We use short-pulse lasers as drivers in electrical circuits and can get an electronic response 10 times faster than what is capable with any other techniques,” Grischkowsky said, describing the work of his Ultrafast Terahertz Research Group at OSU. “This lets us generate a new class of beams that are not light or radar beams, though they’re probably more like radar than light, in an altogether different frequency, or wavelength.

“We’re looking at the world in a different color than what most people have ever looked at it,” he said.

The group’s efforts to demonstrate the sensitivity and effectiveness of terahertz time-domain spectroscopy have involved dozens of experiments and led to more than 130 journal publications with more than 6,000 citations.

“When I first started, people used to say, ‘Yeah, you can make a measurement, but we can do that in other ways. You’re just using your laser, high tech technique to do what we can do already,’” Grischkowsky said. “Superficially, that was true, but we later proved we could make the same measurements enormously better.”

Never-before seen places the group has explored using terahertz radiation include the far-infrared adsorption spectrum of a flame, part of an unprecedented study that had not been possible with existing measurement techniques.

“We were interested in what molecules could be seen in our frequency range, and the idea was to try to find radicals and unstable molecular entities and define these products of combustion,” Grischkowsky said. “Our spectrum was dominated by water vapor, and we could see, for the first time, the line strengths and line widths of water vapor at temperatures above 2,000 degrees Fahrenheit.”

The hybrid technique the group uses to generate terahertz radiation may impact areas from medicine and health and defense and homeland security to communications. Engineers and scientists are exploring the use of terahertz radiation in medical imaging due to its propagation characteristics, including line of sight travel and the ability to penetrate tissue, and the fact that unlike X-rays it does not damage DNA or cells. Its ability to penetrate clothing, wood, cardboard, plastics, masonry and ceramics suggests that terahertz radiation also can support package inspection and tracking, security screening and detection of concealed weapons. It is also hypersensitive to explosive, biological and chemical agents.

Combining lasers and microchips they custom design and fabricate in their laboratory’s clean room in OSU’s Advanced Technology Research Center, Grischkowsky, faculty members Alan Cheville and Weili Zhang and their students in the School of Electrical and Computer Engineering have developed some of the world’s fastest performing optoelectronics for many research applications. Working with IBM researchers, they demonstrated the possibility of transmitting information at data rates approaching 1 terabit per second, a factor of 200 times faster than today’s high performance fiber-optics.

And as part of radar ranging studies for the military, the group demonstrated how terahertz radiation can be used to determine enemy warplane radar signatures precisely using miniature, scale-sized models instead of the actual aircraft.

Grischkowsky, whose latest collaboration with the U.S. Naval Research Laboratory will be the cover article for an upcoming issue of the Journal of Physical Chemistry, is inspired by the chance of discovery, however, and not necessarily the opportunity to define future uses of terahertz radiation. He views his Ultrafast Terahertz Research Group’s investigations as adventures beyond the usual spectrum in pursuit of new knowledge.

“We’re trying to deliver the equivalent of a new telescope or a new microscope with capabilities that are better than other approaches for a whole class of problems,” he said. “As we try to establish this new technology, we embark on an experiment expedition in a certain area, but we don’t know exactly what we are going to find.

“Our work in terahertz science and photonics is about trying to understand the technology, and once you do that, it will lead to fruits of application”