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