PNNL-13501 - Pacific Northwest National Laboratory

Study Control Number: PN00056/1463
Infrared Chemical Sensor Development
David M. Sheen, Bret D. Cannon, Jim F. Kelly
Detecting and characterizing chemical vapors is important for detecting the proliferation of weapons of mass destruction.
Coherent lidars or ladars can provide substantially enhanced sensitivity for detecting chemical vapors with narrow-band
absorptions, or phase information that contains velocity, vibration, and turbulence parameters, associated with scattering
targets.
Project Description
This project developed sensitive, non-cryogenic
technologies for detecting important effluents such as HF,
HCl, and HCN, which constitute a class of compounds
analyzed in the mid-infrared (optical wavelengths from 3
to 18 microns). These are difficult effluents to detect
because their absorption features are very narrow, so
traditional methods of hyperspectral imaging cannot be
exploited to do wide-area plume detection and sensitive
identification.
The objectives of this project included: 1) developing
coherent spread-spectrum lidars, such as frequency
modulated differential absorption lidar, for
detecting/identifying vent plumes and characterizing the
phase properties of the plumes (velocity, vibrational
spectrum, turbulence; etc.); and 2) mating the lidar with a
passive imaging spectrograph to enhance the plume
imaging capability of hyperspectral imaging passive
sensors.
Introduction
Detecting the phase information is relevant to vent
location, targeting, and other functions. The short-wave
infrared (optical wavelengths between 1 and 3.5 microns)
atmospheric transmission windows are especially useful
for detecting halogenated-acids and -hydrocarbons, and
this wavelength region also offers excellent reflectance
returns from the Earth’s surfaces that make remote
sensing practical. We are studying the application of
short-wave infrared technologies, first developed for fiber
communications to make high-duty cycle, narrow-band
coherent lidar and ladars for applications in wide-area
vent location. We are also studying the suitability of
mating these lidars with passive dispersive sensors to
perform hybridized vent imaging and identification of
important halogen acids and cyanogens.
Initially, this research had three distinctive tasks that have
relevance to infrared chemical sensing:
1. system concept development, consisting of
numerical model development and use of the models
to identify promising system concepts
2. quantum cascade laser heterodyne chemical
sensing, in which signals from frequency modulation
formatted infrared quantum cascade lasers were
studied for efficient signal recovery after scattering
from rough surfaces
3. short-wave infrared chemical sensing
instrumentation, which involved development of
suitable short-wave infrared lidars and passive sensor
platforms to detect halogen-acids, in the lower
troposphere.
We decided to involve many other laser architectures and
avoid possible collateral technology channeling effects
should the supply of quantum cascade lasers become a
critical impasse. We also decided to study the effects of
propagation and scattering under realistic field conditions.
The instrumentation developed in the third task was to be
studied to confirm theoretical and bench-scale
measurements in the first two tasks.
Results and Accomplishments
System Concept Development
An extensive numerical model for remote infrared
chemical sensing using frequency modulation
spectroscopy was developed (Sheen 2000). This model is
a mathematical tool for predicting the performance of
laboratory and field prototype frequency modulation
chemical detection systems as applied in various detection
scenarios. Components of the model include: modulation
source, transmitter laser, transmitter optics, atmosphere,
target, receiver optics, detector and preamplifier, and
Sensors and Electronics 397