Electron density and temperature determination of a laser-induced plasma in hydrogen gas

In dense plasmas that contain hydrogen, electron number densities can be deter- mined from the measured full widths at half maximum of the Balmer lines. Electron temperatures can be inferred from Boltzmann plots of the Balmer series. These techniques are applied to characterize the temporal evolution of the electron number density and temperature of a plasma generated by a pulsed laser in pure hydrogen gas. The excitation source is a pulsed Nd:YAG laser which has a wavelength of 1.064 µm and a temporal pulse width of 7.5 ns. The average energy per pulse is 150 mJ.

Using time resolved spectroscopy, electron number densities in the range of 10¹⁶ to 10¹⁹ cm^-3 are inferred for the first few microseconds of the plasma decay. The corresponding temperatures range from approximately 5,000 K to 15,000 K. The time resolution of these results is 6 ns for the electron temperatures and 2 to 100 ns for the electron number densities.