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Overview:
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
zhangxc@rpi.edu
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