Melting Steel With Solar Power

potential of any powerful device.

refering to a device built hundreds of years ago. I don't think he is saying that it should be used as one.

Light and all the caloric energy must be concentrated at a focal point, which is located at a certain distace AWAY from the lens or (in this case) mirror. the lens acts as an aplifier of the enegry, and it doesn't melt because the highest temperatures occur only at the focal point.

the otherhalf of the truth is that the light must be absorbed to heat something, cause it is a lense it is allowed to pas throught un obstructed which causes minimal heating

A weapon that could only be used in sunny weather, has extemly short range, can be defeated by a smoke screen, fragile, large and ungainly, to big to comoflage, can only fire at stationary targets, ect, ect, ect. No military on the planet would want one.

but can't it evaporate enemy satellites passing by in orbit ? how about assembling an array of such ray-guns in space itself to shoot down the enemy ?

...lets see how good a "weapon" this makes..
1) too big to move easily (area of collection enormous if high heat wanted)
2) can you steer it - well maybe but generally only a few degrees either side ofthe suns pathway across the sky
3) can you get your target to sit at focus (doubt it) - moving focus? not at these energies
4) Oh yeah ...what happens on a cloudy day

that's why this would be not much of a weapon

above.