The Jet Fighter Laser Cannon
fahrbot-bot sends in a Register piece about DARPA issuing the penultimate contract for what is intended to be a jet-mounted laser cannon. The Reg outdoes itself in a BOTEC involving downsizing to shark scale. "The US military will shortly issue a brace of contracts for 'refrigerator sized' laser blaster cannons. One of the deals will see a full-power ground prototype built which will be the final stage prior to America's first raygun-equipped jet fighter. ... If it scales down far enough, this would seem to put handheld HELL-guns within an order of magnitude of the striking power offered by conventional small-arms. A 9mm pistol bullet has about 750 joules muzzle energy: a 5kg portable HELL-ray weapon would put out this much energy in a blast less than a second long. ... A dolphin can carry a human being weighing up to 100kg along for a ride. A thoroughbred shark in good training can surely match this. Thus, we seem to be looking at practicable head-[laser] output in the 20-kilowatt range."
All it would have to do is heat up the fuel tanks to combustion. It may not even have to do that, the thermals on jet fighter engines are insane. The exhaust leaves at far greater than the melting temperature of the alloy the engines are made out of. Therefore all sorts of tricks like laminar airflow cooling are used. However, an external source of heat into the system could totally mess up those cooling techniques...