Why do laser weapons in sci-fi have color and how could they be controlled?

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AnthreX
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i have been wondering...
the guns there r like red laser guns
1.if u want to kill the person why did u have to put the colour to it ?

i thought lasers don't have a colour

and the lightsabre that's just weird..
2.how can a laser stop ??

3.is it even possible to control its length ?
4.and again there is colour is there a colour so we can see ?
 
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Lasers emit radiation which is essentially monochromatic, ranging over a fairly wide range of frequencies from infrared to ultraviolet. There are lasers which emit radiation sufficiently intense to burn through metal plates.
 
AnthreX said:
i have been wondering...
the guns there r like red laser guns
1.if u want to kill the person why did u have to put the colour to it ?

No color is necessary, but there's no reason it couldn't be colored. High energy photons are probably more effective, so blue or violet would be the more powerful colors. Ultraviolet of x-ray lasers are even more powerful, and those colors are invisible to the human eye.

i thought lasers don't have a colour

Sure they do, though infrared lasers and x-ray lasers don't have color that you can see. But you shouldn't be looking into laser beams anyway.

and the lightsabre that's just weird..
2.how can a laser stop ??
3.is it even possible to control its length ?

I always preferred phasers myself.

As for how can a light sabre be of a certain length, it's done by superimposing laser pulse trains so they destructively interfere past the end of the sword. The control circuitry is a closely guarded secret of the Aldebaron Amalgomated Corporation, as is the ultracompact power supply. Now that's the real trick, since they can't use dilithium crystals (which only exist in a galaxy a far trek away from the Star Wars worlds).
 
Lasers are so highly focused that no photons are lost to the periphery, so unless the laser is shot into your eye, or there is some dispering force (such as fog) in the path of the beam, you shouldn't be able to see it.
 
I have another thought why would you even need a light sabre if darth vader confronted me with a light sabre id pull out my gun and shoot a bright red beam through his hanibal lecter helmet