In this work coherent Thomson scattering (TS) is used to investigate thermal plasmas composed of single inert gas species and a mixture of inert gas and metal vapor species, since this technique allows electron temperature and density measurements independent from the heavy plasma particles (ions and neutrals). The experimental setup is adapted to perform measurements on stationary as well as transient processes. Therefore thermal plasmas generated by a DC gas Tungsten arc welding (GTAW) process using Argon as a shielding gas and pulsed gas metal arc welding (GMAW) process using Aluminum welding wire and Argon as a shielding gas can be investigated. The results of the measurements are used to estimate the concentration of the metal vapor in the plasma arc.