The tool of choice during the 1990s was a device that sampled the air using paper swabs that changed color depending on the agent detected. The M256A1 chemical agent detection kit, one of the emblematic pieces of equipment of the first Gulf War, detects nerve gas, mustard gas, and other agents believed to be in the Syrian arsenal. These kits are now widely used by civilian first responders and available for sale to the public. The system is easy to use but prone to false alarms?and there are only so many pieces of paper available.
So in 2004, the Pentagon set up the Joint Chemical Agent Detector program to develop more sophisticated methods. The Pentagon ordered $52 million of one new system: the M4A1 ion mobility spectroscopy devices from Smith Detection in 2008. These devices, which can clip into a soldier's belt, work by heating gases to release ions, and then tracking the speed at which those ions travel to identify the chemical. The system is still improving, and this April the U.S. Army placed a $27 million order for enhanced M4A1s. The company says deliveries have already started.
Defense intelligence has its own high-tech gear to detect chemical weapons from a distance. The Portable Hazard Observation System (PORTHOS) uses infrared beams to detect and identify hazards. Just point the device at a target and peer through the viewfinder?the long-wave infared beams can analyze vapors from as far as 3 miles. It works because the gas is at a different temperature than the surrounding air; the detector reads the spectra to determine what kind of gas is present and displays the name of the agent in the viewfinder. And the whole system can be mounted onto a UAV. Expect more detection devices to be installed on ground and aerial robots, as well as remotely operated stations protecting airfields and forward operating bases.
Still, there is a demand for something soldiers can take with them. Block Engineering, the company that makes PORTHOS, annunced this month it is joining Johns Hopkins University to build a handheld version of the system. The engineering challenge is to shrink the hardware into a package that weighs half as much as the current system.
The future of chemical detection may be lasers, where industry and government researchers are devising new ways to detect chemical weapons. For example, just this week U.S. Army Research lab scientists published a paper in the journal Optics Letters that details a new way to measure low concentrations of weaponized gases. The system uses laser photoacoustic spectroscopy, which identifies agents by the way they sound when heated and cooled by lasers.
Usually this form of detection works at only one frequency at a time, and can detect only one kind of chemical agent at a time. But the ARL physicists intertwine three lasers at various frequencies, generating differing reactions from a range of sources. By comparing the acoustics these gases generate as they heat and cool against a database of known threats, the new sensor could one day provide instant identification of many kinds of chemical weapons.
The trick here is to create the right kind of laser. The researchers need a quantum cascade (QC) laser array with at least six mid-infrared laser wavelengths?which has not yet been invented. QC lasers harness photons (and create beams) by dropping light waves to increasingly lower energy levels. The benefit is that these lasers are more compact and powerful than a traditional diode, and the beam can be harnessed at controllable energies.
These powerful lasers are becoming more common in defense hardware; currently simple QC arrays are used in antimissile jammers. "There are groups of researchers producing QC laser arrays that will operate with sufficient power," ARL physicist Kristan Gurton says. Soon they may also be able to create enough beams for the ARL detector to work.
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