Boston Chapter of the IEEE Photonics Society

Wed
Oct 12, 2005
8:15 PM
 

MIT Lincoln Laboratory
 

Chemical Recognition & Remote Sensing in the Terahertz Region

Dr. Mark G. Allen, Physical Science Inc., Andover, MA

Abstract:  New sources in the THz spectral region  permit accessing the unique spectroscopic signatures of gases, liquids, and solid materials.  In many cases, these spectroscopic signatures may be probed while the material is enclosed in a package that is opaque to traditional light sources.  Thus, new opportunities for chemically-specific sensors in both in-situ and stand-off, or remote sensing, configurations are possible.  This tutorial will begin by exploring the intra- and inter-molecular origin of spectroscopic signatures in selected gases, liquids, and solids.  It will also describe the transmission spectra of many common packaging materials and highlight spectral regions where through-packaging inspection of chemical substances may be possible.  Much basic spectroscopic data in the THz region is acquired through laboratory studies using pulsed, broadband THz sources derived from mode-locked visible lasers.  The tutorial will explore the use of laser-based THz sources for quantitative spectroscopic measurements, including the time-domain formulation of the complex Beer's Law, methods for optimal numerical filtering of frequency inversions, and experimental methods for reliable and repeatable spectroscopic measurements of condensed phase materials in time-domain measurement systems.  Differential Absorption LIDAR techniques are being adapted for use as  standoff sensors in the THz spectral region.  The tutorial will discuss general approaches to this problem, especially with respect to THz emitter selection, atmospheric spectral windows for long-distance transmission, and signal processing algorithms.  The use of THz QCL's in these applications will be analyzed in detail.

Biography:  Dr. Allen received his B.S. with honors in Mechanical Engineering in 1981 from the University of Kentucky.  He received M.S. (1982) and Ph.D. (1987) degrees) in Mechanical Engineering from Stanford University under the guidance of Prof. Ronald K. Hanson.  Since joining Physical Sciences Inc. in 1987, Dr. Allen has continued his research in the development of laser and optical devices, sensor systems, and measurement techniques.  He is currently Vice-President of Photonics at PSI, where he directs research and development of advanced sensor and optical components for defense, security, environmental, medical, and industrial applications.  Dr. Allen is leading the development of practical applications of room-temperature laser technologies based on quantum cascade laser technology for 4.5 - 100 microns, interband cascade technology for 2 - 5 microns, and engineered optical materials for Difference-Frequency-Generation in the 2 - 5 microns spectral region.  He is an author of over 170 papers and presentations in laser-based sensors and spectroscopy.  Dr. Allen is a Fellow of the Optical Society of America, former Chair of the OSA Optical Science Division, and founding co-chair of the OSA Topical Meeting on Optical Terahertz Science and Technology.