Earlier in June this year, military police were deployed to clear a crowd of protestors near The White House. Investigations by NPR have revealed that prior to the clear out, a military police officer sought to know if a 'heat ray' weapon was available with D.C. National Guard. The crowds were dispersed with smoke and tear gas as the latter was not in possession of such weapons.
However, if a military police officer was seeking such a 'weapon', it is likely that he had seen it before and the answer to the question can be found on the Joint Intermediate Force Capabilities Office website, filed under the Department of Defense's Non-Lethal Weapons Program.
Called the Active Denial System (ADS), it is a "non-lethal directed-energy weapon capable of shooting man-sized (5 ft - 1.5 m) beam millimeter waves up to a distance of 3,280 feet (1,000 m)," according to a FAQ page on the website. Unlike kinetic weapons such as rubber rounds that possess a risk of injury, the ADS is uniformly effective regardless of size, gender, and age, the website claims.
Addressing potential concerns, the FAQ page goes on to clarify that the weapon does not use a laser or work as a microwave oven. Instead, at 95 GigaHertz, its frequency is much higher than a microwave (2.45 GHz) and since it is fired for very short durations, it produces only a heat sensation on the skin surface.
The Non-Lethal Weapons Program has spent over 15 years developing the weapon and has conducted over 13,000 exposures of the waves to determine that it is still safe and does not cause blindness or cancer. Rather the system is developed to automatically limit the fire duration, the program claims.
The system is very much legal as per the laws in the U.S. and currently, there are two system configurations available for the weapon. The first is a robust mobile system transported by Marine Corps MVTR truck while another is an armored, containerized system transportable by tactical vehicles, the website said. Both systems have completed thorough military utility assessments and can be deployed quickly if a request is received.
For future developments, the U.S. Army is working on solid-state monolithic microwave integrated circuits to improve the size, weight, and cooling on the ADS that will allow integration into various mobile platforms. Gallium nitride (GaN) is more efficient than silicon for integrated circuits, the website stated further.