Nanofabrication of tailored surface structures in dielectrics using temporally shaped femtosecond-laser pulses

We have investigated the use of tightly focused, temporally shaped femtosecond (fs)-laser pulses for producing nanostructures in two dielectric materials (sapphire and phosphate glass) with different characteristics in their response to pulsed laser radiation. For this purpose, laser pulses shaped by third-order dispersion (TOD) were used to generate temporally asymmetric excitation pulses, leading to the single-step production of subwavelength ablative and subablative surface structures. When compared to previous works on the interaction of tightly focused TOD-shaped pulses with fused silica, we show here that this approach leads to very different nanostructure morphologies, namely, clean nanopits without debris surrounding the crater in sapphire and well-outlined nanobumps and nanovolcanoes in phosphate glass. Although in sapphire the debris-free processing is associated with the much lower viscosity of the melt compared to fused silica, nanobump formation in phosphate glass is caused by material networ...