Laser tanks are impractical. What if the enemy wears mirrored shades? That laser goes right back and kills you instead. You don't want your 100 million dollar tank to be taken out by a pair of Ray-Bans.
The Army has officially deployed a pair of high-energy lasers overseas to blast incoming enemy drones out of the sky, the service recently confirmed, marking a major milestone for the U.S. military's ongoing development of futuristic directed-energy weapons.
The 20-kilowatt Palletized High Energy Laser, or P-HEL, "is currently deployed to support the Army's mission" in an undisclosed location abroad, a spokesman for the service's Rapid Capabilities and Critical Technologies Office, which manages its directed-energy portfolio, told Military.com.
I think the bigger concern is enemy UAVs wearing shades.
The moment those mirrors stop being perfectly shiny they begin thermal collapse. Which is the real reason mirrors exposed to the atmosphere can't be used as targeting optics.