Dual-Wavelength Interferometric Measurement of Electrically Exploded Aluminum and Copper Wires in Low-Pressure Air for Electron and Ion Density Calculation

Electron and atomic densities of Cu and Al plasmas in low-pressure air are studied using the recently reported dual-wavelength (1064 and 532 nm) interferometric diagnostic. The electrical explosion of a 99.999% pure, straight wire forms cylindrical plasma volumes within a low-pressure air chamber, and the probing lasers' interferometry patterns are simultaneously recorded at prescribed times after wire explosion. The measurements are performed repeatedly from 50 to 1200 ns in 50-ns increments allowing the calculation of electron and ion densities and the observation of the plasma's expansion and dissipation. The densities are calculated from fringe line analysis using a signal-processing-based algorithm that automatically extracts the fringe ratio. Finally, the maximum average volumetric electron and ion densities are calculated. The results of atomic density agree with past reports but are two orders greater than electron density, which suggests that full ionization is unattained.