Postdoctoral fellow Dan Eakins
Laser Pulses That Can "See" Improvised Explosives
October / November 2009
Volume 7 Number 5
A passion for stopping terrorists" is how Los Alamos National Laboratory scientist David Moore of the laboratory's Shock and Detonation Physics group describes his drive to search for new and better technologies to detect improvised explosives. Moore and his team, along with their Princeton University collaborator, are currently working on an innovative laser technology called Optimal Dynamic Detection of Explosives, or ODD-Ex, that shows promise as a highly reliable "stand-off" explosives detector that can "see" very small quantities of explosive molecules at considerable distances, but is blind to most of the background noise in the signal.
The technology depends on "shaped ultra-fast laser pulses" coupled with "machine learning," an idea first investigated at Los Alamos to enhance the safety of explosive detonations by initiating the explosion "intelligently" at low power and at specific wavelengths.
"I got interested originally through a need to detect trace amounts of explosive constituents in the search for environmental contaminants," said Moore. "Because most of today's technologies are very inefficient and prone to false-positives, we started looking for ways not to enhance the signal, but to suppress the background noise."
This new technique is based on an emerging capability to control phenomena known as "quantum molecular dynamics" with advanced laser pulse shaping. This is combined with high-volume adaptive experiments guided by special mathematical algorithms.
Because it is easily adaptable, ODD-Ex seeks out the best laser pulse shapes to maximize sensitivity and selectivity of potential explosive materials. As a result, the interrogating laser pulse is specifically shaped to create a maximum signal from the explosive materials while minimizing the signals from background interference. A key goal of the research is to achieve optimal detection performance by fully exploiting the flexibility of ultrafast laser pulse shaping technology.
All molecules, when exposed to specific kinds of energy, will vibrate. The shaped ultra-fast laser pulses are tuned to excite specific molecules—€”like the nitrates in explosives—€”and report back what they're found.
As an example, Moore describes a scenario where officials are trying to determine if a fingerprint on a car door contains specific explosive constituents. "There are going to be fatty acids in the fingerprint, a variety of other compounds present on the door, and the paint and other coatings are going to absorb certain wavelengths of light," said Moore. "This technology would give us the ability to shape the laser pulse so it only communicates with the explosive materials and ignores everything else."
Moore's team includes Margo Greenfield, Jason Scharff and Shawn McGrane of the Shock and Detonation Physics group at LANL, and Herschel Rabitz of Princeton University.
Kevin Roark is a communications specialist for Los Alamos National Laboratory.
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