Thomson scattering from a laser induced breakdown in 1 atmosphere of helium

Summary form only given. Studies of the shape and separation of He I allowed and forbidden lines can give valuable information about the electron density in astrophysical and laboratory plasmas . Most of these studies rely on Stark broadening theories where self-absorption of lines can be quite limiting and result in incorrect values of n_e. Using diagnostics such as Thomson scattering can help in overcoming this problem, as well as test the Stark broadening approaches. Thomson Scattering is one of the most powerful diagnostic tools for plasma characterization and it has been applied to a variety of plasmas. It is a non-intrusive technique and the interpretation of the signal is relatively simple. However, this method has not been widely applied in studies of laser induced breakdown in gases [2], We will present our recent experimental results in this area. Optical Thomson Scattering has been used in the study of laser induced breakdown in He gas at 1 atm. The experiment has been carried out using two Nd:YAG lasers. An Nd:YAG laser (E=850mJ) operating in the first harmonic regime (1064nm) was used to breakdown the He, and a frequency doubled (532nm) Nd:YAG (E=100mJ) was used to probe a slice of the plasma.