Xi-Cheng Zhang, the J. Erik Jonsson ’22 Distinguished Professor of Science and director of the Center for Terahertz Research at Rensselaer Polytechnic Institute, has received the William Streifer Scientific Achievement Award from the IEEE Photonic Society. The award honors Zhang for his exceptional contributions in the past 10 years to the field of lasers and electro-optics.

“Dr. Zhang’s work is literally changing the way in which we can see the world and all that it is made of,” said Rensselaer Acting Dean of Science David Spooner. “His research and development of terahertz technology has broken new ground in the field of photonics time and again and has implications for science, industry, law enforcement, and even counter-terrorism efforts. We are exceptionally proud of his many achievements.”

The award is given for a single, recent contribution to photonics that has greatly influenced the research community. Zhang was cited “for the exceptional contribution of terahertz air photonics, especially free-space coherent detection of ultra-broadband terahertz waves.”

Terahertz (THz) waves occupy a segment of the electromagnetic spectrum between the infrared and microwave bands. As such, they can be used for imaging and sensing in ways that are not possible with conventional technologies such as X-ray and microwave. Because THz radiation transmits through almost anything that is not metal or liquid, the waves can “see” through most materials that might be used to conceal explosives or other materials, such as packaging, corrugated cardboard, clothing, shoes, backpacks, and book bags. They are also safer than X-rays and microwaves for human tissue.

The vast potential of terahertz-based technology has been understood for years, but the development of practical applications of THz was greatly limited by something as simple as air. Ambient moisture in the air outside of a highly regulated lab environment blocks THz wave transmission. This made it nearly impossible to apply THz technology outside the controlled lab setting up until now.

Zhang’s development of THz air photonics has resulted in the discovery of several important THz techniques:

• THz Air-Biased-Coherent-Detection (THz ABCD). Instead of fighting with the properties of the air, the technology developed by Zhang works with it. This technique uses air and selected gases as the THz wave emitter. A focused optical pulse creates atmospheric plasma, which produces very strong and ultra-broadband THz waves.
  
  
• THz-Enhanced Acoustics (TEA) and THz-Enhanced Fluorescence (TEF). The development of remote, spectroscopic sensing technologies for THz waves are lagging behind important real-world needs such as the detection of explosives in airport baggage. Zhang and his students have developed THz-enhanced acoustic (TEA) and THz-enhanced fluorescence (TEF) techniques with standoff sensing capability. By “hearing” THz-enhanced acoustics (TEA), or “seeing” THz-enhanced-fluorescence (TEF), coherent detection of THz waves at standoff distance has been achieved.
  
  
• Control of THz Wave Polarization. Zhang and his team developed a unique method to harness THz wave polarization. The polarization of THz pulses emitted from a laser-generated air-plasma can be rotated by changing the relative delay between ultra-short two color (red and blue) pulses.

Zhang joined Rensselaer in 1992. He received his bachelor’s in physics from Peking University in China and both a master’s and doctoral degree in physics from Brown University. He is a fellow of the American Physics Society, the Institute of Electrical and Electronic Engineers, and the Optical Society of America. He is an NSF CAREER Award winner who has been featured in more than 80 magazines, 28 books and book chapters, and 300 journal papers. He holds 26 U.S. patents.

The Technology Review listed Zhang’s work in as one of “10 Emerging Technologies That Will Change World” in 2004. The History Channel and Discovery Channel have interviewed Prof. Zhang for their Modern Marvels and The Greatest Gadget programs. Zhang’s instrument development was also selected as one of the “Scientific American 50” in 2008.

More information of the Center for Terahertz Research can be found at http://thz.phys.rpi.edu.