The quantum cascade laser is a special kind of semiconductor laser, usually emitting in the mid- and long-wave infrared bands. Such a laser operates on laser transitions not between different electronic bands but on intersubband transitions of a semiconductor structure. Their wide tuning range and fast response time allow for faster and more precise compact trace element detectors and gas analyzers that are replacing slower and larger FTIR, mass spectroscopy, and photothermal microspectroscopy systems.
Applications include detecting chemical warfare agents and toxic industrial chemicals, monitoring building air quality, measuring greenhouse gases for atmospheric research, monitoring and controlling industrial processes, analyzing chemicals in exhaled breath for medical diagnostics, and many more. Compact, portable trace gas sensors enable operation in a wide range of platforms, including handheld units for use by first responders, fixed installations for monitoring air quality, and lightweight sensors for deployment in unmanned aerial vehicles (UAVs).
Most quantum cascade lasers emit mid-infrared light. However, quantum cascade lasers can also be made for generating terahertz waves. Such devices constitute very compact and simple sources of terahertz radiation. Recently, even room temperature terahertz generation has been achieved via internal difference frequency generation.
Improvised Explosive Devices (IEDs) are often made of compounds that absorb in the terahertz range; ruggedized and portable THz QCL-based detectors could be continuously scanned ahead of a moving convoy or used to search a public gathering space for threats.
QCLs are increasingly being used to detect, identify, and measure levels of trace gases in the air e.g. for detecting very small concentrations of pollutants in air. Such systems measure the unique infrared absorption “fingerprints” of chemicals to provide high detection sensitivity and identification confidence, and are particularly useful for field-portable sensing. This property is also useful to intelligence agencies for detecting chemical warfare agents.
QCL-based systems are also finding application in the growing field of medical diagnostics. Trace gases present on a patient’s breath can indicate diabetes, asthma and other respiratory issues, kidney and liver dysfunction, and other indicators are being discovered regularly. Such an application requires extremely fast sampling times, relatively small size, and accurate results in order to avoid misdiagnosis.
QCL enables standoff detection in battlefield as well as many civilian applications where it is not possible to locate the sensor in the near vicinity of the dangerous source. “Standoff detection of trace chemicals, such as explosive residues, chemical warfare agents and toxic industrial materials, is a critical unmet need within the Intelligence Community, Department of Defense, and Department of Homeland Security,” commented Dr. Anish Goyal, Block’s VP of Technology.
Quantum cascade laser (QCL) systems also support military applications such as Infrared Countermeasures (IRCM) and targeting. The demanding product requirements for aircraft platforms that include reduced size, weight, power consumption and cost (SWaP-C) extends to portable, battery powered handheld products.
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