In the past it was possible to Lock on a TITAN AT Launcher to a Laser from a Laser Designator. This seems not the case anymore. You can "Soft"-lock the Laser with your Launcher as seen in Screenshot 1. (Often a lock is hard to achieve altough theres clear line of sight to the laser but thats probably another problem). There will be no beeping or a solid lock visual. Once fired the rocket will ignore the lock and just fly by wire.
Before you could a solid lock, audio signal and the missile tracked the laser as seen in Screenshot 2.