updated 2/23/2011 10:48:19 PM ET 2011-02-24T03:48:19

It’s not just magicians who can make something appear out of thin air; researchers can do it, too. A group at Princeton University has developed a way to shoot a laser beam at a specific point in the air where a second beam is created that can travel in the reverse direction.

The so-called “air laser,” could work to sample chemicals in the air and warn military personnel about the presence of dangerous hidden explosives in war zones or help environmentalists determine how many greenhouse gases a power plant is releasing.

To work their magic, researchers use a laser-generating machine to excite oxygen molecules, which release energy in the form of photons. Mirrors inside the machine focus the photons into a beam of ultraviolet light and direct it to a specific point in the air, similar to the way a magnifying glass focuses sunlight.

Once the ultraviolet laser beam reaches its destination, the energy is so concentrated that the beam excites oxygen atoms at the focal point. Just like in the machine, the oxygen atoms release energy in the form of photons. This time, the photons carry infrared radiation instead of ultraviolet because the energy in the focused laser is not as strong as the laser-generating machine and, therefore, cannot excite the oxygen atoms to the same level.

More importantly, the shape of the beam forces the atoms at the focal point to concentrate and release their photons in the reverse direction, creating a new laser in the air that returns along the same path the first laser went out on. Because the returning laser appears to be created out of thin air rather than inside a machine, it has earned the term “air laser.”

“It’s kind of like having a laser pointer that creates a beam that comes back at you when you shine it into the air,” said Richard Miles, the lead researcher and a professor of mechanical and aerospace engineering at Princeton University.

Scientists can compare the chemical signature of the return laser to the original one and see if there have been any changes.

Miles said the return laser, which is less than a millimeter in diameter, could provide better readings of chemicals in the air compared to other lasers. For example, in a light detection and ranging or LIDAR method, a laser is bounced off an object and scatters the laser particles throughout the air. Some of these particles make it back to the starting point where researchers can then collect chemical readings.

Furthermore, a LIDAR method can measure how many chemicals are in the air, but it cannot identify which chemicals they are.

But instead of dispersing throughout the air, chemicals picked up with photons in an air laser return with directly to the original starting point, providing a good sample for analysis that has the potential for precise identification.

Arthur Dogariu, a research scholar in Princeton’s Department of Mechanical and Aerospace Engineering, said the next step is to develop a way to identify the types and amount of chemicals being sent back.

“Now that we’ve demonstrated that is works well, we are looking at how we are going to detect molecules, he said.

Once the team does this, Dogariu said, the technology could be used for many practical uses like detecting chemicals from gas leaks in homes or office buildings or detecting chemicals that could be used in terrorist threats.

Currently, the U.S. Navy funds the project, which began two years ago. Miles said they hope to use the technology to remotely detect hidden bombs. Bombs release small amounts of chemicals into the air, and if a laser could “sniff out” these chemicals, military personnel would know when a bomb was in the area. It will take large amounts of time and money to develop the laser to this level, but Miles said for the Navy, it’s worth it.

“The payoff of being able to detect these things and save a few lives is a very highly motivating reason to build them,” he said.

Phillip Sprangle, the chief scientist at Research Naval Laboratory in Washington D.C., has worked with lasers for decades and was not associated with this project. He said the research does not account for real-world variables like air turbulence.

“It was conducted in the laboratory under ideal conditions, so there are a lot of practical issues,” he said.

Sprangle said the “air laser” is a great accomplishment that could help researchers understand more about remote detection. But, he said, many more questions need to be answered before the research will have any tangible effects.

“It’s going to require many big steps forward and this is just one,” Sprangle said.

© 2012 Discovery Channel


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