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Lasers Boost Standoff Sensing

Photonics.com
Mar 2012
OAK RIDGE, Tenn., March 26, 2012 — 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  


GLOSSARY
hyperspectral imaging
Methods for identifying and mapping materials through spectroscopic remote sensing. Also called imaging spectroscopy; ultraspectral imaging.
lidar
An acronym of light detection and ranging, describing systems that use a light beam in place of conventional microwave beams for atmospheric monitoring, tracking and detection functions. Ladar, an acronym of laser detection and ranging, uses laser light for detection of speed, altitude, direction and range; it is often called laser radar.
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
quantum cascade laser
A Quantum Cascade Laser (QCL) is a type of semiconductor laser that emits light in the mid- to far-infrared portion of the electromagnetic spectrum. Quantum cascade lasers offer many benefits: They are tunable across the mid-infrared spectrum from 5.5 to 11.0 µm (900 cm-1 to 1800 cm-1); provide a rapid response time; and provide spectral brightness that is significantly brighter than even a synchrotron source. Quantum cascade lasers comprise alternating layers of semiconductor...
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