|Postcard from Laser weapons|
The question came up again recently - how effective would a laser weapons be?
Well, the US has been working on directed energy weapons for quite some time, and in 2014 a laser was installed on the USS Ponce, and the UASF planned to mount a chemical laser in a Boeing 747 to shot down incoming ballistic missiles. In tests, there were usability issues arising from the chemicals used. There are a variety of vehicle mounted lasers, the Zeus is usable against mines and others are intended for crowd control.
So, yes, laser weapons are in the early stages of what most people would call "working".
Then someone brings up Star Wars and lasers in space and the discussion is a little different.
Lets start with Star Wars. Much as I like the franchise, whatever is being fired isn't a laser. It moves too slowly - people can actually dodge the beam or use a "light sabre" to intercept it.
So what about more realistic lasers in space, based on the developments referred to above? For a start, the beam won't be visible. You can see a laser on Earth because there's an atmosphere to reflect portions of the beam. In a vacuum, there's nothing to reflect it, so it won't be visible.
Because the beam travels at the speed of light, the target won't know it's being shot at until it's hit. If it's close to the source of the beam, it's not going to be able to manoeuver to avoid more hits once it knows that it's under attack. This gives the attacker a clear benefit.
If the separation between the two is too great, then the laser looses some of it's usefulness. Because the edges of the beam aren't quite parallel, it spreads out as it travels. At short distances, it's not a problem, but in space it's beam spread will limit the effective range. At the distance of the moon you're likely to have a searchlight rather than a weapon, so the science fiction battles where lasers are effective at great distances between space craft aren't likely.
Of course, it's possible that in a century I could be proven wrong, but I can live with that.