Exploration of the fundamental "damage limit" light flux for grazing incidence liquid metal mirrors

One definition for the "damage limit" of a liquid metal surface used as a f inal optic for laser fusion power plants is the maximum energy flux that th e liquid metal can withstand without any resulting spallation. Some prelimi nary calculations were performed by Moir to roughly estimate the damage lim it by imposing the restriction of a 200 degreesC surface temperature rise. Here, new 1D calculations that account for hydro-motion on the compressible time scales are presented, along with revised estimates of the damage limi ts for liquid aluminum, sodium, and mercury. Slow compression time scales ( similar to 20 ns) produced negative pressures in the liquid film on the ord er of MPa, and fast ignition time scales (similar to 10 ps) yielded GPa pre ssures for the laser energy densities set out by Moir. For Na and Al the pe ak energy densities normal to the beam on the order of 5 to 10 J/cm(2) were acceptable for fast ignition when 85 degrees grazing incidence is assumed. Some experimental data on the generation and damping of surface waves resu lting from surface ablation recoil is also presented, where large waves are seen to damp out after about 50 ms following the laser pulse.