Standoff sensing enters new realm with dual-laser technique

Mar 22, 2012
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. This figure was selected for the cover of Journal of Physics D: Applied Physics.

( -- Identifying chemicals from a distance could take a step forward with the introduction of a two-laser system being developed at the Department of Energy's Oak Ridge National Laboratory.

In a paper published in the Journal of Physics D: , Ali Passian and colleagues present a technique that uses a to "pump," or strike, a target, and another to monitor the material's response as a result of temperature-induced changes. That information allows for the rapid identification of chemicals and .

"With two lasers, one serves as the pump and the other is the probe," said Passian, a member of ORNL's Measurement Science and Systems Engineering Division. "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 use of a second laser provides a robust and stable readout approach independent of the pump laser settings."

While this approach is similar to radar and lidar sensing techniques in that it uses a return signal to carry information of the molecules to be detected, it differs in a number of 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."

This work represents a proof of principle success that Passian and co-author Rubye Farahi said could lead to advances in standoff detectors with potential applications in quality control, forensics, airport security, medicine and the military. In their paper, the researchers also noted that measurements obtained using their technique may set the stage for hyperspectral imaging.

"This would allow us to effectively take slices of chemical images and gain resolution down to individual pixels," said Passian, who added that this observation is based on cell-by-cell measurements obtained with their variation of photothermal spectroscopy. Hyperspectral imaging provides not only high-resolution chemical information, but topographical information as well.

Explore further: Neutron tomography technique reveals phase fractions of crystalline materials in 3-dimensions

More information: The paper, titled "Pump-probe photothermal spectroscopy using quantum cascade lasers," is available at:

Related Stories

Tunable quantum cascade laser

Jul 07, 2010

( -- One of the issues associated with lasers is their tunability. In many cases, if you want to produce a particular wavelength, you have to build a laser to accomplish this. In order to get another wavelength, ...

Catching cancer's spread by watching hemoglobin

Apr 30, 2007

In an advance that can potentially assist cancer diagnosis, a new optical technique provides high-resolution, three-dimensional images of blood vessels by taking advantage of the natural multiple-photon-absorbing properties ...

Building a more versatile laser

Nov 16, 2009

( -- One of the drawbacks associated with using semiconductor lasers is that many of them can only produce a beam of a single wavelength, and can only send that beam in one direction at a time. ...

Finding explosives with laser beams

Feb 27, 2012

Scientists at Vienna University of Technology have found a way to detect chemicals over long distances, even if they are enclosed in containers.

Recommended for you

50-foot-wide Muon g-2 electromagnet installed at Fermilab

23 hours ago

One year ago, the 50-foot-wide Muon g-2 electromagnet arrived at the U.S. Department of Energy's Fermi National Accelerator Laboratory in Illinois after traveling 3,200 miles over land and sea from Long Island, ...

Spin-based electronics: New material successfully tested

Jul 30, 2014

Spintronics is an emerging field of electronics, where devices work by manipulating the spin of electrons rather than the current generated by their motion. This field can offer significant advantages to computer technology. ...

User comments : 0