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 spectr al measurements of the hydrogen Balmer series are reported and analyze d to characterize the electron number density and excitation temperatu re of the decaying plasma. The electron density is inferred from the S tark broadened H-alpha linewidths; excitation temperatures are estimat ed using Boltzmann plots of the Balmer series. In the first few micros econds following laser breakdown, electron densities are found to be i n the range of 10(19)-10(16) cc(-1), with corresponding excitation tem peratures in the range of approx. 100,000-6600 K.