Supercritical Density Profiles of CO2-Laser-Irradiated Microballoons

Electron-density profiles up to $40n_c$ have been measured for plasmas produced on glass microballoon targets irradiated by nanosecond, C${\mathrm{O}}_2$-laser pulses in the intensity range 2×${10}^{12}$ to 6×${10}^{13}$ W ${\mathrm{cm}}^{-2\mathrm{}}$. Critical-density scale lengths of ∼ 3 μm and plateau structures, including overdense bumps, have been observed. Upper-shelf densities were greater than those attributable to radiation pressure alone, possibly indicating contributions from the superthermal plasma blowoff and self-generated magnetic fields.