A newly developed two-laser system will enable scientists to identify biological agents and chemicals from a distance. Researchers at the US Department of Energy’s Oak Ridge National Laboratory devised a technique that uses a quantum cascade laser to strike or pump a target while a second laser monitors the thermal response of the material. The measurements derived from the method can be used for the rapid evaluation of biological agents and chemicals for military, forensics, airport security, medical and quality control applications. An infrared pump laser scans a region of interest of the sample, and an accompanying probe laser reads out the absorption spectrum of the constituent molecules. An image can thus be formed that represents the molecules making up the sample surface. (Image: Office of Science) “With two lasers, one serves as the pump, and the other is the probe,” said Ali Passian, an ORNL researcher. “The novel aspect to our approach is that the second laser extracts information and allows us to do this without resorting to a weak return signal.” The second laser provides a stable, robust readout approach that is independent of the pump laser’s settings. Although comparable to lidar and radar sensing techniques, this approach is different in certain ways. “First is the use of photothermal spectroscopy configuration where the pump and probe beams are nearly parallel, Passian said. “We use probe beam reflectometry as the return signal in standoff applications, thereby minimizing the need for wavelength-dependent expensive infrared components such as cameras, telescopes and detectors.” The two-laser system could lead to advanced standoff detectors, and measurements obtained using the technique may set the stage for hyperspectral imaging. The work appeared in the Journal of Physics D: Applied Physics. For more information, visit: www.science.energy.gov