One weapon they are working on uses a “laser-induced plasma effect,” which sees a high-powered laser being fired to create a ball of plasma. A second laser is then shot to oscillate this plasma, which has the effect of creating sound waves. When enough of these bursts are fired from the laser at the right frequencies, the vibrations of the plasma will sound just like human speech. This technology could be used by military personnel to target specific people with warnings or messages without putting themselves at risk.
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