Opacity measurements in shock-generated argon plasmas

Dense plasmas having uniform and constant density and temperature are generated by passage of a planar shock wave through gas. The opacity of the plasma is accurately measured versus wavelength by recording the risetime of emitted light. This technique is applicable to a wide variety of species and plasma conditions. Initial experiments in argon have produced plasmas with 2 eV temperatures, 0.004--0.04 g/cm3 densities, and coupling parameters Γ∼0.3--0.7. Measurements in visible light are compared with calculations using the HOPE code. An interesting peak in the opacity at 400 nm is observed for the first time and is identified with the 4s-5p transition in excited neutral argon atoms. copyright 1994 American Institute of Physics