This is in response to posts in a thread below, since the original topic was about a NOVA special I felt it was best to start a new thread on the topic.

DISCLAIMER: While the following is rather detailed, it reveals NOTHING that isn't freely available information.

How could lasers be used against planes as a terrorist weapon?

The idea is that lasers could be used to blind/disable a pilot. This is feasable ONLY if the plane is in the process of landing- to do this while a plane is in mid flight is not practical.

How would a terrorist do it?

Well, first you have to pick your laser. You want something compact, and high power output. Additionally, you do NOT want it to be visible. A visible beam would be visible from a great distance due to rayleigh scattering, and would point to the perpertrator like an arrow... also if the intended victims sees something painfully bright they will blink thereby possibly reducing the damage inflicted. If the laser used is not visible then by the time its effect has been noticed the maximum damage has been done. The first warning sign will be that the victim can no longer see.

The invisibility requirement means the laser has to be in the Ultra-violet or infra-red wavelengths. Ultra-violet lasers have poor air transmission and would be seriously attenuated by cockpit windows, so that leaves IR wavelengths. You want to use a wavelength that will pass through the cornea and lens so it can do maximal damage to the retina of the victim. All these wavelength requirements narrow down your choices to Near Infra-red lasers.

You need a laser that is portable. If you use it repeatedly from a fixed location you will only be able to use it a few times before flights are halted and you are possibly caught. Optimally you want something that can be transported and used in a vehicle. This requires that the power consumption is low- so you want a high efficiency laser.
Diode lasers have the highest wall-plug efficiency... The following laser meets the above requirements:

http://www.els.de/Products/DiodeStar.html

It is high power (300 Watts), compact, invisible (900+ nm wavelength), low power consumption... It would fit in a modest size van, and would require a portable generator capable of providing a few kilowatts.

How would it be used?

The most likely method of attack would be to transport the laser to within a few miles of a major airport- at night (there are several good reasons for doing the attacks at night I will mention the reasons later on). If planes are landing from the north then you want to be South of the airport. You will have to have built your own projection optics and controls. This is not simple but certainly not impossible- you want an IR sensitive camera looking out along your beam, this is your targeting sight. Your projection mirror could be controlled by a joystick. The IR camera would move with the projection mirror.

The 3 main reasons for doing this at night are:

1 The obvious one is that it makes for fewer witnesses.

2 At night the pilots pupils will be dialated, increasing the damage inflicted. Pilots at night would not be wearing any sunglasses.

3 The IR camera used for targeting will probably work better.

You acquire a landing plane on your camera. You wait Until the plane is committed to landing yet still fairly far away from the runway and then turn on the laser. You can use the camera to guide the beam onto the target. The plane is landing, coming towards you so its apparent motion relative to you is fairly slow. Keeping on target would not be hard. You would aim for the cockpit front windows, directly into the eyes of the pilots.

If you project 300 Watts in a spot 2 meters in diameter you will likely illuminate the entire cocpit crew and at the very least impair them severely. If you go with a 1 meter spot you quadruple the intensity, a 50 cm spot would probably result in complete long term if not permanent impairment to anyone struck in the eyes. They would be trying to land blind- unable to see the instruments or the runway. The victims would be in a panic and in physical pain. You would slowly dither the spot back and forth across the cockpit windows in order to ensure all were affected.

Passive Counter-measures

There are nearly no defensive countermeasures that can be taken without knowing the wavelength of laser that is being used. If the wavelength is known then protective goggles can be used by pilots during landing. These goggles would impair night vision somewhat, but are better than blindness.

A single terrorist with such a setup could roam from airport to airport taking out one or two planes (Airports would rerout planes after 1 or 2 crashes in a short period of time) at each airport. This would disrupt the air travel industry until the terrorist was caught. A group of terrorists with such weapons operating nation wide would shutdown air traffic nationwide for an inderminate amount of time. It could very easily be more disasterous to the airlines and economy than 9-11.

Active Counter-measures

These too would be limited.

Law enforcement might take a while to understand the nature of the attack, once known it would likely be a short time before the vendor that sold the lasers was identified. Not a lot of these kind of lasers are sold every day- once the wavelength was identified then protective goggles could be ordered and issued. If the terrorists use weapons at several different wavelengths then this becomes less effective.

The best defense is to make computerized pilotless landing possible- not a cheap solution. Airports could be eqipped with IR cameras to detect the use of such a weapon and locate its position.

Equipping a group with many such lasers would be VERY expensive (lasers like this are in the 6 figures). Making them weapons would take technical skill and more money.

Again, this isnt really a 'how to' manual, just putting together a few obvious facts into a scenario.