Laser system technology identifies trace chemicals in the air

A team of researchers from the USA has designed a novel laser system technique that allows identifying electric charges and chemicals of interest with unprecedented sensitivity. Such laser technology may find a potential laser application for scanning vast areas for radioactive material or dangerous chemicals for safety and security aims.
This laser technique, called mid-infrared picosecond laser-driven electron avalanche, registers very low charge densities (the number of electric charges in a specific volume) in the air or other gases. Thus, the laser system technology makes it possible to measure electron densities in the air created by a radioactive source at levels below one part per quadrillion, that is equal to picking out one free electron from a million billion conventional air molecules.
The principle of operation is based on the use of method enabling to calibrate laser systems applied to examine irradiated air from 1 meter away. Herewith, the researchers confirm that such laser technology could be used to identifying other chemicals and species and could be improved for remote detection at distances of 10 meters and even 100 meters.
It should be noted that the laser system technique uses a process of electron avalanche, in which a laser beam accelerates a single free electron in gas until it achieves enough energy to knock a different electron off a molecule, resulting in a second free electron. Also, the electron avalanche process repeats and converts into a collisional cascade that grows exponentially until the appearance of bright observable spark in the laser beam focus.
Despite the fact that the method of laser-driven electron avalanche is not new, however, this is a new kind of high-energy, long-wavelength laser system — a picosecond mid-IR laser that is able to detect localized collisional cascades seeded only by the initial free electrons. Herein, it is possible to generate the original free electrons seeding the avalanches directly by laser protons when shorter wavelength laser beam pulses are applied.
Finally, this laser system technology overcomes conventional Geiger counters and scintillators, traditional detectors of radioactive decay products because it resolves the problems of signal dropping distances far from the radioactive source. Nonetheless, a laser beam allows researchers to remotely examine electrons created in the air near the source.
Also, the researchers affirm that potential applications of the laser technique include the measurement of ultra-low charge densities from such sources as strong field physics interactions or chemical species. Nevertheless, the presented laser technology is not ideal and requires improvements to make the technique more practical for use in the field.
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