Multiple phase change of lead oxide film for optical storage

The authors used a PbO thin film incorporated in a trilayer anti-reflection structure for write once and read many (WORM) optical storage. The medium, both with and without an in-contact protective overcoat, showed multiple levels of reflectance change after low-power laser writing at 6328 AA wavelength. The multiple levels of reflectance changes correspond to multiple phase changes due to the PbO film going through PbO (massicot), Pb 3 O 4 (minium), PbO 1.37 , PbO (litharge), PbO (massicot) phases and then melting in the temperature range up to 700 degrees C. There is a possibility of formation of PbWO 4 phase when the absorber layer is tungsten.