Optical Particle Trap for Real-Time Detection of Threat Agents

Schematic of the confocal laser beam trap (B) The laser profile of the trapping hollow cone (C) A particle is trapped at the focal point. Figure courtesy of Optics Letters via DTRA

Characterizing a particular harmful agent in the air can be difficult, delaying response time to a biological or chemical incident or attack.

The Optical Particle Trap (OPT), developed by the Defense Threat Reduction Agency’s Joint Science and Technology Office, traps and distinguishes individual particles from the surrounding atmosphere, making for quicker identification and a speedier and more accurate response to threats.

Collaborators from the U.S. Army Research Laboratory and 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.

Read more: Elastic Back-Scattering Patterns Via Particle Surface Roughness and Orientation from Single Trapped Airborne Aerosol Particles.

Article adapted from original by the Defense Threat Reduction Agency’s Chemical and Biological Technologies Department, edited for context and format by CBRNE Central.