Pulse of infrared light created by air laser  (Source: Image courtesy Arthur Dogariu, Princeton University)
Laser sensor is 1,000 times more powerful than LIDAR

The U.S. military is spending significantly on research into the use of lasers as weapons and sensory devices. A research program funded by the Office of Naval Research at Princeton University has announced a significant breakthrough in the use of lasers as sensors.

The research team has developed a new laser that may be able to detect bombs and pollutants from a long distance. The breakthrough is called the Air Laser. Richard Miles, professor of mechanical and aerospace engineering at Princeton said, "We are able to send a laser pulse out and get another pulse back from the air itself. The returning beam interacts with the molecules in the air and carries their finger prints."

The technique uses a laser beam shot at a target and the beam excites a cylinder of air as it passes that is only a millimeter wide. The region that the beam passes through is a hot spot that creates excited oxygen atoms that have electrons pumped up to high energy levels. As the laser pulse ends, the electrons fall back down and emit infrared light. That light passes back through the cylinder that the original laser beam created and transmits back to the original point of origination for the laser beam. A sensor at the originating spot would be used to receive the beam that comes back to the source and determine what contaminants it encountered on the return trip to the sensor.

Miles said, "In general, when you want to determine if there are contaminants in the air you need to collect a sample of that air and test it. But with remote sensing you don't need to do that. If there's a bomb buried on the road ahead of you, you'd like to detect it by sampling the surrounding air, much like bomb-sniffing dogs can do, except from far away. That way you're out of the blast zone if it explodes. It's the same thing with hazardous gases – you don't want to be there yourself. Greenhouse gases and pollutants are up in the atmosphere, so sampling is difficult."

A technique that is similar to what the Princeton team has developed already in use today is LIDAR. LIDAR is used to measure density of clouds and pollutants in the air. The problem is that LIDAR isn’t sensitive enough to detect trace amounts with accuracy. The Princeton method developed is about a thousand times more powerful than LIDAR.

The much stronger beam will allow the scientists to measure the trace elements encountered on the way back. Those trace elements could be atmospheric pollutants or vapors released by explosives.

Miles said, "We'd like to be able to detect contaminants that are below a few parts per billion of the air molecules. That's an incredibly small number of molecules to find among the huge number of benign air molecules."

The Navy's laser platform for destroying missiles in flight was announced to be 9-months ahead of schedule last week.

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