I wonder what the energy output ratio needs to be in order to engineer a self sustaining system. At 2:1 output to input it seems the scale would have to be impractically massive to cover all the inefficiencies in systems necessary to convert output heat to electricity and keep powering the Laser.
Natural fusion in the heart of stars requires massive amounts of gravity.
The will not achieve the required energy output with lasers.
Magnetism, maybe, but not lasers............