In this contribution we summarize the work of our team in the last years, which is devoted to the principle, development and applications of a new spectroscopic technique: two photon polarization spectroscopy. This technique is suitable for the diagnostic of plasmas even in far off thermodynamic equilibrium conditions. Up to now, working with hydrogen and deuterium in different kind of media, such as laboratory plasmas or industrial flames, we have been able to measure the absolute density and kinetic temperature of the hydrogen atoms, the electric field in the dark space of a hollow cathode discharge, and the Stark broadening of the 2S level of hydrogen isotopes. The full potential of this technique requires tuneable pulsed high power UV laser radiation of single longitudinal mode. To achieve this powerful tool we have modified a commercial laser and we will pay special attention to this system. The whole experimental arangement provides plenty of new and promising possibilities such as the study of industrial interest elements like oxygen, carbon, or nitrogen.