ELECTRON NUMBER DENSITY AND TEMPERATURE-MEASUREMENT IN A LASER-INDUCED HYDROGEN PLASMA

A Nd:YAG laser operated at 1064 nm and 7.5 nsec pulse duration is used to create optical breakdown in gaseous hydrogen. Time-resolved spectral measurements of the hydrogen Balmer series are reported and analyzed to characterize the electron number density and excitation temperature of the decaying plasma. The electron density is inferred from the Stark broadened H-alpha linewidths; excitation temperatures are estimated using Boltzmann plots of the Balmer series. In the first few microseconds following laser breakdown, electron densities are found to be in the range of 10(19)-10(16) cc(-1), with corresponding excitation temperatures in the range of approx. 100,000-6600 K.