ABSTRACT
Terahertz (THz) wave sensing and imaging have received a great deal of attention in the past decade owing to its signicant scientic and technological potentials in various multidisciplinary elds. However, two major challenges were present in the development and application of remote open-air broadband THz spectroscopy in addressing the urgent needs of homeland security, the elds of astronomy, and environmental monitoring: (1) Due to the limited performance of existing emitters and sensors in the far-infrared
CONTENTS
Overview .............................................................................................................. 142 THz Wave Air Photonics .................................................................................... 144
Generation in Plasma ..................................................................................... 144 Detection in Plasma ....................................................................................... 145 Experimental Setup ........................................................................................ 146
All-Optical Standoff THz Wave Detection ...................................................... 147 Experimental Details ...................................................................................... 147 Remote Sensing .............................................................................................. 148 Ionization Process ........................................................................................... 148
THz Wave Time-Domain Spectroscopy ........................................................... 150 Applications and Trends .................................................................................... 152
Biomedical Imaging ....................................................................................... 152 Explosive Identication ................................................................................. 153 Pharmaceuticals .............................................................................................. 155 Food Safety ...................................................................................................... 156 Handheld THz Instrumentation .................................................................. 156
Applications in Defense ............................................................................ 159 Industrial Applications ............................................................................. 160
Conclusions .......................................................................................................... 161 Acknowledgment ................................................................................................ 162 Bibliography ........................................................................................................ 162
(IR) range, there was a THz gap, and (2) due to strong water vapor absorption, remote sensing with broadband THz waves was considered impossible. The requirement for on-site bias or forward collection of the optical signal in conventional THz detection techniques has inevitably prohibited their use in remote sensing. An “all-optical” technique of broadband THz wave detection has been recently developed to tighten the mentioned gap. The technique is based on coherent manipulation of the uorescence emission from asymmetrically ionized gas plasma interacting with THz waves. Unique features of measured THz pulses at standoff distances (30 m) are minimal water vapor absorption and unlimited directionality for optical signal collection. This chapter presents an introduction to the THz wave air photonics technique, along with its applications in various elds such as biomedical imaging, explosive identication, pharmaceuticals, food safety, defense, and security.
