Simultaneous measurement of electron and heavy particle temperatures in He laser-induced plasma by Thomson and Rayleigh scattering

Thomson and Rayleigh scattering methods were applied to quantify the electron and heavy particle

temperatures, as well as electron number density, in a laser spark in helium at atmospheric

pressure. Plasma was created using 4.5 ns, 25 mJ pulses from Nd:YAG laser at 532 nm.

Measurements, performed for the time interval between 20 ns and 800 ns after breakdown, show

electron density and temperature to decrease from 7.8 x 10²³ m^-3 to 2.6 x 10²² m^-3 and from

95 900K to 10 350 K, respectively. At the same time, the heavy particle temperature drops from

only 47 000K down to 4100K which indicates a two temperature plasma out of local isothermal

equilibrium.