And they're not going to be anything like they are in science-fiction and fantasy. With blindness, invisibility of attack, instantaneous hits, and extreme heat? Much more scary, actually.
In any case, I rather doubt laser weapons will get much use at ground level, if only because of rain/various kinds of active smoke you can use to defend yourself.
I'd imagine, because of the problems with atmospherics, before we see ground-level lasers we'll see shorter-range UAV-to-ground weapons. Perhaps satellites first. Silent invisible death from the sky.
US infantry tactics as they currently exist will not be well-suited to wars involving such weapons; a retired Marine gunnery sergeant, H. John Poole, has written a number of books on the need for the US to develop autonomous light infantry, and has pointed to the prospect of laser weapons as one of the reasons for this need.