Jane's has a good overview of the ray gun world's state of play. The bits about the problems facing the beam-firing 747, the Airborne Laser, and the blaster-equipped cargo plane, the Advanced Tactical Laser, are particularly juicy.Full-on flight tests of the Airborne Laser, or ABL, have been pushed back to 2008. But "some aspects of the system cannot be demonstrated on the ground," Jane's notes. "Laser performance in real high-altitude conditions and the performance of the entire system at high altitudes. As in a rocket, the chemical systems in the COIL [chemical oxygen iodine laser, the ABL's weapon] are affected by atmospheric pressure at the exhaust outlet, which creates back pressure in the flow path."
Another issue is logistics: hydrogen peroxide is corrosive and a powerful solvent of organic materials (including people) and potassium hydroxide is a toxic material used as a drain cleaner and (by Norwegians) to preserve codfish. Neither is used by any other military system, so the chemicals require new storage and transport facilities and special training and handling procedures...The USAF's other airborne COIL project is the ATL [Advanced Tactical Laser], which has a budget of $200 million [and] is due for high-power flight tests in mid-2007, aboard an C-130H platform.ATL has a much lower power goal than the ABL - in the tens of kilowatts rather than megawatts - and is intended to disable rather than kill its targets, demonstrating the ability of lasers to achieve specific, ultra-precise effects. The design reference missions for ATL are to stop a moving vehicle and disable a communications node from 10,000 ft.Stopping a vehicle does not necessarily mean destroying it or killing its occupants. If the laser can penetrate the engine cover, for example, the temperature within the engine compartment is likely to get higher than is mechanically optimal. The laser could penetrate the fuel tank and start a fire. In the case of a communications target, cables and antennas could be the weak spots.Delivery of hardware for the ATL... started during 2005 and the C-130 platform was delivered to Boeing in January this year... Unlike the ABL, the ATL does not vent harmful gases into the atmosphere: the exhaust is ducted into a container of activated carbon, which absorbs and neutralises it.While ATL presents less risk than ABL, it is more likely to be overtaken by other developments: primarily, the development of more powerful solid-state lasers. The attractions of a solid-state laser - which uses a solid transmissive material as the lasing medium - are clear, notes AFRL's Hamil: the 'magazine' can be as deep as the aircraft's fuel tanks (which can be replenished in flight) and there are no exotic fuels to handle and no chemical exhaust. The disadvantage is that solid-state lasers today do not have the power to do anything other than illuminate. At high powers, 'thermal lensing' - the change in optical qualities with heat - becomes what Hamil calls "horrific", making it difficult to produce a high-quality beam.(Big ups: Eric)