First responders have the need to quickly assess a situation; Understanding if there are biological or explosive hazards
present can influence a plan of action. The need for real-time information, however, precludes most laboratory analysis
techniques. The requirement of not disturbing a sample until it is understood makes the problem even more challenging.
Visual identification can go a long way in assessing a threat, and now technologies in the mid-infrared (2 to 20 μm)
spectral region allow extending that "vision" into a spectral region known for its chemical identification capabilities.
This paper considers the fusion of tunable quantum cascade lasers with infrared focal plane arrays to create a true
chemical imager. Instrumentation is developed that allows real-time chemical analysis of residues and powders in a noncontact
fashion. Identification of explosive residues and biological powders are considered as examples of use of this
new technology for first responders. As opposed to many fielded technologies that allow only point detection of
substances, and often require many seconds to analyze a sample, mid-infrared chemical imagers provide context in
addition to sample analysis in real time. They are also ideal for image fusion techniques combining visual images with
chemical images from an infrared multispectral analysis. This type of chemical overlay on live video provides first
responders with a powerful tool for rapid threat assessment.
Micro- and nano-technologies (MNT) have opened up the mid-infrared (IR) spectral region to room temperature
techniques that are enabling new applications in chemical imaging. The mid-IR is rich in wavelength specific
absorptions that can be used to identify different chemicals and materials. It is only in the last decade, however, that mid-
IR cameras and tunable, intense mid-IR laser sources have become available that are compact and operate at room
temperature. MNT has allowed these developments; micro-bolometer arrays are now routinely fabricated with 25 μm
resolution and the ability to sense mid-IR radiation from 7 to 14 um. Quantum cascade (QC) lasers fabricated with
exquisite control of semiconductor layers and waveguides serve as the gain media for tunable mid-IR lasers, some even
tuned with MEMS feedback elements. The current state of mid-IR imaging and illumination is discussed, and specific
examples of its use in chemical imaging are presented. First, passive mid-IR imaging is considered, along with its ability
to be used for chemical identification. The use of tunable mid-IR lasers as an illumination source is then considered.
Technical aspects of illumination and detection paradigms are presented, with a consideration of how spectroscopic
information gathered in both stimulated thermal emission and reflectance modes can be analyzed to determine chemical
composition in an image. Finally, specific examples of QC laser assisted chemical imaging are presented.
Broad tunability in the mid-IR (~3-12 μm) is desirable for a number of applications. We have built a number of External
Cavity quantum cascade Lasers (ECqcLTM) that maximize tuning range from the quantum cascade chip. As much as 525
cm-1 of pulsed and 121 cm-1 of cw, mode hop-free tuning has been obtained. Various mechanisms for the broadening of
the gain of the QC chip are considered.
Commercially available quantum cascade semiconductor materials continue to mature. When integrated into external
cavity quantum cascade laser (ECqcL™) geometries, these laser systems are now providing near-continuous coverage
throughout the entire 3 - 13 μm regime. Such coverage enables molecular detection systems to enjoy high sensitivity
and selectivity. Individual lasers have been demonstrated to provide > 320 wavenumbers of tuning. Wide tuning ranges
have also been demonstrated at wavelengths in the 3 - 4 μm regime. In addition, phase continuous (mode-hop-free)
tuning allows for extremely high resolution spectroscopy to be performed throughout the mid-IR. Daylight Solutions
will review the most up-to-date results regarding wavelength coverage, tuning range and power levels achieved from
ECqcL™ systems. Daylight will also provide recent results in sensitivity and coverage from their multi-species Swept
Sensor™ and photoacoustic detection platforms.
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