Two-dimensional mapping of the electron density in laser-produced plasmas.

We performed two-dimensional (2D) mapping of the electron density in a laser-produced plasma with high spatial and temporal resolution. The plasma was produced by irradiating an aluminum target with 1064 nm, 6 ns pulses from a Nd:YAG laser under vacuum conditions. Stark broadening of the lines was used to estimate the electron density at various locations inside the plasma. The 2D spectral images were captured at different spatial points in the plasma using an imaging spectrograph coupled to an intensified CCD at various times during the plasma expansion. A comparison between radially averaged and radially resolved electron density profiles showed differences in the estimated values at the earlier times of plume evolution and closer distances to the target. However, the measured radially averaged values are consistent with 2D radial profiles at later times and/or farther distances from the target surface.