THz Optoelectronics: Sensing

Work in the lab of Terahertz (THz) Center Director Xi-Cheng Zhang is focused on THz optics and optoelectronics. The terahertz region of the electromagnetic spectrum, loosely defined by the frequency range of 0.1 to 10 THz (1012 cycles/second) has proven to be one of the most elusive. Situated between infrared (IR) light and microwave radiation, it is resistant to the techniques commonly employed in these well-established neighboring bands. High atmospheric absorption constrained early interest and funding for THz science, limiting the major domain of THz spectroscopy to spectral characterization of the rotational and vibrational resonances and thermal emission lines of simple molecules by chemists and astronomers. As advanced materials research provided new and higher power sources over the past 20 years, the potential of THz for advanced physics research and commercial applications was demonstrated, revolutionizing THz systems.

Terahertz spectroscopy systems utilize far-infrared radiation to extract molecular spectral information in an otherwise inaccessible portion of the electromagnetic spectrum, allowing a material's far-infrared optical properties to be determined as a function of frequency. This information can yield insight into material characteristics for a wide range of applications, making THz Optics sensing an extremely attractive research field with interest from sectors as diverse as the semiconductor, medical, manufacturing, space, and defense industries.

Technical Description:
Terahertz spectroscopy is a promising modality for material diagnostics for samples ranging from semiconductors to biomolecules. One of the major methods employed by Zhang is THz time-domain spectroscopy. THz time-domain spectroscopy, which grew from work in the 1980s at AT&T Bell Labs and the IBM T.J. Watson Research Center, uses short pulses of broadband THz radiation, typically generated using ultrafast laser pulses. While the spectral resolution of THz time-domain spectroscopy is much coarser than narrowband techniques — and its spectral range significantly less than that of conventional Fourier Transform Spectroscopy — it has several advantages that have given rise to a number of important recent applications. The transmitted THz electric field is measured coherently, which provides both high sensitivity and time-resolved phase information. Typical THz time-domain spectroscopy systems have a frequency bandwidth between 2 and 5 THz, a spectral resolution of 50 GHz, an acquisition time under one minute, and a dynamic range of 1x105 in electric field.

Contact Information:
Xi-Cheng Zhang
Director, Center for Terahertz Research

Professor, Department of Physics, Applied Physics and Astronomy
Professor, Department of Electrical, Computer and System Engineering
Erik Jonsson Chair Professor of Science
Rensselaer Polytechnic Institute,
110 8th Street
Troy, NY 12180-3590 USA

(518) 276-3079