Warfighters must be prepared for the unthinkable, such as the release of a chemical or biological weapon. But characterizing a particular harmful agent in the air can be difficult, delaying response time.
The Optical Particle Trap (OPT), developed by the Defense Threat Reduction Agency's Joint Science and Technology Office is changing that by providing warfighters with accurate, real-time detection of airborne chemical and biological agents.
The OPT will allow warfighters to trap and distinguish individual particles from the surrounding atmosphere, making for quicker identification, enabling a speedier and more accurate response. This new capability is another step closer to being able to collect detailed, real-time data on a single particle during a chemical or biological attack.
Yong-Le Pan, Ph.D, from the U.S. Army Research Laboratory, highlighted the accomplishment in the Journal of Quantitative Spectroscopy and Radiative Transfer article, “Elastic Back-Scattering Patterns Via Particle Surface Roughness and Orientation from Single Trapped Airborne Aerosol Particles.” Pan and fellow researcher Joshua L. Santarpia, Ph.D., from Sandia National Laboratories, utilized OPT to demonstrate a method to simultaneously measure the back-scattering pattern and image of a single laser-trapped airborne aerosol particle. Building on previous work, the device traps one particle, which is between 10-50 μm in size, using a laser beam.
The first beam uses optical radiative pressure force and photophoretic force to stabilize the particle in place and then utilizes a second beam for particle illumination and manipulation. This system allows the researchers to trap a particle independent of its charge for several hours. Researchers also have the ability to manipulate the particles as they travel through the device, allowing for rapid analysis via elastic light scattering.
The overall method of trapping and measuring provides information on the back-scattering patterns, which change with particle size, shape, surface roughness and orientation. Elastic light scattering is sensitive to individual aerosol particle properties such as density, size, shape, complex refractive index and surface roughness. Because of its sensitivity, elastic light scattering could provide real-time, on-site aerosol identification, especially in monitoring life-threatening bioaerosols when mixed with normal atmospheric background constituents.
This method can provide unique back-scattering signatures on micron-sized particles. In addition, it may be used to provide backscattering information for a light detection and ranging (LIDAR) application, since many real-time applications operate in a LIDAR configuration.
Currently, OPT is undergoing testing in which researchers are analyzing how different environmental factors such as high humidity and concentration of organic carbons in the atmosphere affects specific types of aerosol particles. Experimental data will feed into predictive models for hazard assessment and detection development capabilities for protecting the warfighter.