Boston Chapter of the IEEE Photonics Society

Wed
Oct 19, 2005
8:30 PM
 

MIT Lincoln Laboratory
 

Terahertz Devices for Imaging and Sensing

Prof. James Kolodzey, University of Delaware, Newark, DE

Abstract:  During the past few years, the terahertz frequencies, spanning roughly from 0.3 THz to 15 THz (1 millimeter to 20 microns in wavelength), have become actively investigated for see-through imaging and materials identification.  As one of the remaining poorly understood “gaps” in the electromagnetic spectrum, the terahertz frequencies are beginning to open up new opportunities for science and for practical applications.  Depending on the application, terahertz offers important advantages, but has some disadvantages.  For imaging, THz is more selective than x-rays and is more sensitive to the nature of the materials it passes through.  Millimeter waves are generally not chemically sensitive, and their longer wavelength translates into lower image resolution.  The oscillator strengths of rotational and vibrational excitations of molecules increase with frequency as f2 or f3, giving terahertz better sensitivity.  Infrared has the disadvantage that scattering is proportional to f4 and THz has greater penetration through aerosols, clouds, and solids. The upper THz range offers unique spectral features that may identify compounds for homeland security.  The atmospheric attenuation is relatively high, however, compared to the infrared and millimeter wave regions.  Novel devices such as the quantum cascade laser, and impurity based emitters and detectors have made terahertz systems more compact and versatile.  Semiconductor based THz devices have increased their operating temperatures to above the reasonable limit of 77 K, and have increased their output powers to above 1 milliWatt.  Competing techniques such as time domain pulsing have the advantage of being broadband and operating at room temperature, but require bulky femtosecond lasers for excitation and they emit relatively low powers.  To be competitive for spectroscopy, semiconductor sources will need to be tunable or operate at multiple emission lines.  This talk will review the state of the art in terahertz emitters and detectors, and will give some details on impurity based devices for imaging and spectroscopic applications.

Biography:  Prof. James Kolodzey received his Ph.D. in electrical engineering from Princeton University in 1986 for research on SiGe alloys.  Previously, he worked at IBM Corporation on optical communications, and at Cray Research on GaAs circuits.  From 1986 to 1990, he was an Assistant Professor of Electrical Engineering at the University of Illinois at Urbana-Champaign, where he established laboratories for cryogenic studies of high frequency devices, and the molecular beam epitaxy of InGaAlAs devices.  In 1987, he spent a year at AT&T Bell Labs with A.Y. Cho.  In 1990, he spent a year at the Technical University of Munich with F. Koch and R. Schwarz.  Since 1991, he has been a Professor of Electrical and Computer Engineering at the University of Delaware.  He studies the electrical and optical properties of nanodevices fabricated from silicon germanium and silicon carbide, alternative gate dielectrics for CMOS circuits, bioelectronic devices, and Terahertz sources and detectors.  In 1997, he spent a year at the University of Paris, Orsay with J.-M. Lourtioz.  In 2004, he was appointed as the Charles Black Evans Professor of Electrical Engineering.  Prof. Kolodzey has co-authored over 150 technical publications.