How SWIFT identifies chemicals in volatile situations
When toxic chemicals are released into the atmosphere, either by accident or in a terrorist attack, authorities need access to accurate information quickly so they can identify the chemicals involved and implement the necessary countermeasures.
Traditional chemical identification technologies such as mass spectrometry or Raman spectrometry are extremely good at their job — they can work with very complex mixtures in very small quantities — but they require close distance to work. The mass spectrometer needs a physical sample of the target chemical, and Raman spectroscopy requires a relatively strong illumination beam that is not eye-safe. This limits the use of these techniques in a potential terrorism situation.
If you want to scan a room or vehicle for target chemicals, scan cargo moving through a monitor station at normal speed, or scan for explosive residue in fingerprints on car door handles, you don't always have the luxury of close-range access to gather a physical sample nor the time it takes to process the sample and identify the chemicals.
Chemical detection from a distance
Supercontinuum Wideband Infrared Fourier Transform (SWIFT) technology, developed by Leidos, overcomes these shortcomings. It can detect any infrared-active chemical, including chemical warfare agents, toxic industrial chemicals, and explosives, from a distance of 50 feet and in concentrations of micrograms per square centimeter. As a result, the sensor technology can be a valuable tool in homeland security applications.
The Leidos solution was conceived as part of the Intelligence Advanced Research Projects Activity (IARPA) Standoff Illuminator for Measuring Absorbance and Reflectance Infrared Light Signatures (SILMARILS) program, which aims to develop a portable system for real-time standoff detection and identification of trace chemical residues on surfaces.
How SWIFT compensates for lack of sample proximity
SWIFT addresses two problems. First, it works despite the challenging physics of sensing at low concentration and long-distance, which is different from a traditional swab sample approach. Second, it uses vibrational spectroscopy technology, a SILMARILS program requirement. While a vibrational spectrometer is by no means the only (or even the most sensitive) way to probe surfaces, it is the most promising approach to doing so at a standoff distance.
In a laboratory situation, a benchtop spectrometer illuminates the sample at very close range using a globar (a thermal light source for infrared spectroscopy) and generates heat and energy across a broad infrared spectrum. However, as you move away from the sample, the light scatters, so you would need an extremely intense globar to make up for that loss. You would also need a way of concentrating the energy on the sample.
The SWIFT solution leverages laser technology to make up for the loss of light due to the sampling distance. Laser light propagates through space much more easily than lamp emissions and can be made to travel in a single direction. This means less dispersion and loss of information.
Lasers typically emit light in a very narrow, single-color band, but SWIFT uses optical nonlinearity to stretch the band out. By doing so, it mimics the wide spectrum one gets from a globar. The pulsed lasers also deliver large and rapid bursts of energy to make up for energy dissipation at long distances, and allow the SWIFT signal to be well above thermal (solar) background during the laser pulse, while still being low enough power on average to be eye-safe.
SWIFT replicates the functionality of a benchtop laboratory spectrometer (its broad spectrum and high energy) but from a distance.
How SWIFT identifies chemicals
Much like a conventional spectrometer, SWIFT showers the surface to be sampled with spectrally broad electromagnetic energy. Some of that energy gets absorbed by the chemicals, so measuring the amount of energy that bounces back over a variety of wavelengths tell us which chemicals are present.
Each chemical has a unique signature for this ratio of sent/returned energy packets. SWIFT matches the measured "reflectance spectrum" with existing ones in its own internal spectral library. A match yields a positive ID in as little as 15 seconds.
Every second counts when chemicals are purposefully or inadvertently released. Accuracy and long-range operational capabilities are both important. SWIFT's ability to sample and quickly identify chemicals from a distance makes it an invaluable asset in sensing technologies in a variety of industries, including in homeland security applications.