>Could it be a focused microwave/radation beam used to heat the surrounding atmopshere into a plasma? Microwave energy is very far outside of the visible spectrum. A microwave beam would not be visible at all and it would not ionize the air at atmospheric pressure. Prior to the development of the laser, exact same principles were applied to produce a device called a MASER which stands for Microwave Amplification by Stimulated Emission of Radiation. It is a coherent beam of single wavelength microwave radiation. It is essentially a very long wavelength laser. Microwave energy, even at very high power levels, would not be able to do ample localized heating as a "traveling wave". Your microwave oven produces localized heating because the interior box of the over is a resonant chamber tuned to the microwave wavelength (about 2450 megahertz). The resonant chamber causes the traveling wave output from the oven's magnetron tube to reflect at the proper length in order to have the wave crests and troughs align in such a way that hey create constructive resonance rather than destructive resonance. Two wave crests meeting in phase will double the amplitude of the wave in that location whereas a wave crest meeting a wave trough will cancel each other out. Though the energy at the meeting points of two crests will double, the points where two troughs meets becomes zero energy so the whole system remains with the same amount of energy it started with. No additional energy is being created in a standing wave scenario, but the effect is to distribute the initial energy to various points in 3D space to provide sufficient energy to make water molecules vibrate violently and produce heat. This wouldn't be practical in a traveling wave scenario because the energy would remain constant at the same input power level and you would need massive amounts of energy to do the same thing a resonant standing wave would do. There is no resonant chamber effect in these pictures, so no, I don't think it could be a microwave energy beam at work here. If you could produce a microwave energy beam of high enough power to set things on fire from great distances without a standing wave resonant chamber, the entire ham radio community would know about it. Such a microwave signal would absolutely disrupt communications in the ~10 to 15 centimeter radio communications band and everyone would know it. You can't hide a signal like that from the many thousands of ears listening worldwide. No matter how tight that beam is, microwaves would still be bouncing around and scattering like crazy and would be detected. It's never been recorded that such a thing has been picked up like that so again I don't think it's possible that microwave energy did this. And by the way, microwaves don't actually heat from the inside out, in case you were wondering.