title: Nonlinear features and response mechanisms of a PtO2 mask layer for optical data storage with a superresolution near-field structure.
abstract: Optical features of a PtO2 mask layer in a superresolution near-field structure are investigated in detail by use of the Z-scan technique. The high photothermal stability of the PtO2 mask is revealed, and a phenomenon in which laser-irradiated PtO2 decomposes to yield Pt particles is confirmed. We also find a physical change in the mask layer that accompanies the chemical decomposition. Microscopic observations and atomic force microscope studies support the theory that the physical deformation is induced by the decomposition of PtO2. It is clear that the optical nonlinear responses of the PtO2 mask layer result from two mechanisms.