Opacity broadening as a density diagnostic for spot spectroscopy

A significant advantage of the recently developed spot spectroscopy techniques for plasma diagnostics is that the blowoff resulting from the tracer dots originally imbedded in the target has a well-characterized size. The helium-like resonance line 1s²?1s 2p¹P may have appreciable optical depth in these blowoff regions, especially near the original target surface. The observed width of this line is largely determined by opacity broadening, which depends directly on the density. Calculations are presented for aluminum, which allow density determination as a function of measured line width. Scaling of the calculations to tracer elements other than aluminum is also discussed.