"Terahertz waves are invisible and just as other electromagnetic radiation types can be pointed to a distant target by means of special antennas and amplifiers. Less than a decade ago a group of scientists headed by Raytheon designed a mighty deterrent system for crowd dispersal that employed unique features of THz waves multiplying their generally 'soft touch' with a extremely powerful generators (gyrotrons) to achieve the desired effect. Officially, it was given the name of Active Denial System (ADS) and it basically represents a directed-energy tool for crowd control, area denial, perimeter security ad similar security -related purposes. Informally, the weapon is also called the heat ray' and it's not without reason.
This technology is based on non-lethal impact on human skin, which in other words does not kill, but scare off people from locations where their presence is unwanted. The technique employs millimeter waves at the frequency of 95 GHz that considerably heat up the very thin top layer of human skin (only down to 0.4mm deep) up to a temperature of approximately 53-54 °C. Such heat ray impact generated by this stand-off deterrent system lasts only for a couple of seconds (or use series of burst 2-sec long), but it's more than enough to achieve the sought result - disperse the crowd. A targeted persons cannot tolerate such effect even for a few seconds, which in its turn forces them to seek escape from its influence and move away."
http://terasense.com/news/active-denial-system-a-terahertz-based-military-deterrent-for-safe-crowd-control/
This technology is based on non-lethal impact on human skin, which in other words does not kill, but scare off people from locations where their presence is unwanted. The technique employs millimeter waves at the frequency of 95 GHz that considerably heat up the very thin top layer of human skin (only down to 0.4mm deep) up to a temperature of approximately 53-54 °C. Such heat ray impact generated by this stand-off deterrent system lasts only for a couple of seconds (or use series of burst 2-sec long), but it's more than enough to achieve the sought result - disperse the crowd. A targeted persons cannot tolerate such effect even for a few seconds, which in its turn forces them to seek escape from its influence and move away."
http://terasense.com/news/active-denial-system-a-terahertz-based-military-deterrent-for-safe-crowd-control/