We investigated laser-based spectroscopic techniques: phase-conjugate degenerate four-wave mixing (PC-DFWM) and laser Thomson scattering (LTS) in terms of their application to Stark profile studies in thermal plasma. PC-DFWM was used for the Stark profile determination while LTS served for plasma diagnostic purpose. Experiments were performed for thermal plasma generated in the transferred arc and burning in pure argon at atmospheric pressure. The spectral profile of the 696.543 nm ArI line was studied. Our attention was paid to the problem of the laser power influence on the measured quantities and plasma state. In the case of PC-DFWM the influence of the laser power manifests itself as broadening of the line profile that can be corrected by a simple extrapolation of the results to the zero laser intensity. On the other hand the results of the Thomson scattering show strong dependence of the electron temperature on the laser intensity and its variations during the laser pulse.