Two-photon photoreduction of metallic nanoparticle gratings in a polymer matrix

We report femtosecond laser nanofabrication using a metal ion-doped polymer. Submicron grating lines arising from two-photon, two-beam interferential fringes were found consisting of photoreduced metallic nanoparticles with diameters ranging from tens to over a hundred of nanometers. The laser-hybrid material interaction was initialized with an in situ photochemical reaction, leading to particle protrusion out of the flat sample surface. A violent change of morphology occurred when the irradiation time exceeded a critical value, producing an abnormal laser ablation image: instead of local material removal, protruding lines are found created at bright fringes. The phenomenon was interpreted as arising from an indirect ablation process.