Phase Transitions Detection Using in Situ Ellipsometry Measurements

Knowledge about the optical properties of materials at high pressure and high temperature is needed for EOS research. The ability to detect phase transitions under a dynamic process is essential. Ellipsometry measures the change in the polarization of a probe beam reflected from a surface. From the change in polarization, the real and imaginary parts of the time dependent complex index of refraction, N(omega) = n + ik, can be extracted. Since the optical properties of materials are related to the electronic and structural properties of materials ellipsometry can be used to detect phase transition. Phase transition detection by ellipsometry was tested with planar impact experiment provided by a gas gun. The optical properties of 1020 steel target under different impact pressure were measured. Changes were measured for shock wave pressures larger than 130 kbar due to the alpha -> epsilon phase transition.