Using a wavelength transformation to send this through the non-absorption windows means more energy hits the ground and you aren't hacking terrestrial albedo in a bad way. That global warming is about absorption of sunlight, so putting a lot more sunlight on the same absorption percent means more heat retained. It doesn't do any good to cut gwp materials in the air, then increase sunlight hitting the atmosphere in a way that makes heat retention higher.

Actually, maser - microwave laser.

The mirror is a fine grid which makes it much lighter and more resilient, and it is much easier to convert into electricity than light.