The original motivation for developing large high power lasers in the inertial confinement fusion (ICF) field was to provide a driver for fusion energy power plants. Consideration of power plant energy budgets leads to a practical requirement for the product of ICF pellet gain G and driver efficiency n to be greater than 10. When pellet gains of 103 were considered realistic, driver efficiencies of 1 to 2% would have been adequate. However, it is now well known that pellet gains are more likely to be in the range 100 to 200, which implies driver efficiencies greater than 5% for economic ICF power plants.
R. J. Jensen,
L. A. Rosocha,
J. A. Sullivan,
"High Power KRF Lasers For Fusion", Proc. SPIE 0622, High Power and Solid State Lasers, (23 June 1986); doi: 10.1117/12.961167; https://doi.org/10.1117/12.961167