The new technique, called mid-infrared picosecond laser-driven electron avalanche, detects extremely low charge densities -- the number of electric charges in a certain volume -- in air or other gases. The researchers were able to measure electron densities in air produced by a radioactive source at levels below one part per quadrillion, equivalent to picking out one free electron from a million billion normal air molecules.
In Optica, The Optical Society's journal for high impact research, researchers from the University of Maryland report using the new method to calibrate lasers used to inspect irradiated air from 1 meter away. They say the approach could be applied to detecting other chemicals and species and could be scaled up for remote detection at distances of 10 meters and, eventually, 100 meters.
Charge - Densities - Method - Daniel - Woodbury
"We can determine charge densities much too low to measure with any other method," said Daniel Woodbury, the lead author on the paper. "We demonstrate the method's ability to detect a radioactive source, but it could eventually be used for any situation that requires measuring trace amounts of a chemical in a gas, such as helping to track pollution, chemicals or safety hazards."
The new technique is based on a process known as electron avalanche in which a laser beam accelerates a single free electron in a gas until it gains enough energy to knock a different electron off a molecule, resulting in a second free electron. This process repeats and develops into a collisional cascade, or avalanche, that grows exponentially until a bright observable spark appears in the laser focus.
Electron - Avalanche - Kind - High-energy - Laser
"Although laser-driven electron avalanche has existed since the 1960s, we used a new kind of high-energy, long-wavelength laser -- a picosecond mid-IR laser -- to enable detection of localized collisional cascades seeded only by the initial free electrons," said Howard M. Milchberg, the research...
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