Dependence of ion charge-energy emission from Nd:YAG-laser-produced plasma on laser intensity in the 0.4–40×10^10 W/cm2 range

We experimentally characterize the ionic emission, including the individual charge states Snz+ (⁠ z=1, …, 8⁠), from laser-produced tin plasma as a function of the intensity of the employed ns-pulsed laser. The plasma is generated in a vacuum from tin microdroplets (diameter ranging from 17 to 35 μm) using pulsed Nd:YAG laser light (laser wavelength λ=1.064 μm) over a range of intensities (0.4– 40×1010 W/cm2). We measure charge-state-resolved and integrated ion energy distributions at seven angular positions around the plasma using seven retarding field analyzers. We highlight peak features in both types of spectra and describe the dependence of their energies on laser intensity with power-law functions. The resulting power laws match those derived from plasma radiation hydrodynamics theory. The analytical scaling laws exhibit strong isotropy, while the ion energy spectra are highly anisotropic.