Nano-groove and 3D fabrication by controlled avalanche using femtosecond laser pulses

We report fabrication of sub-100 nm resolution structures by ablation on the surface of sapphire using femtosecond laser pulses. A single 50-70 nm wide groove was recorded by laser ablation via a controlled ripple formation on the surface. Ripples are created by breakdown due to a sphere-to-plane formation of an ionisation below surface in a similar way as the bulk ripples. Different thresholds for the ripples formed parallel and perpendicular to direction of the laser scan were observed. In a sol-gel photo-polymer SZ2080 and thermo-polymer polydimethylsiloxane, free-standing 3D structures were formed without use of two-photon absorbing photo-sensitizers. Both cases of the surface and bulk structuring were achieved via a controlled avalanche, which dominated ionisation of materials.