Effect of Low Numerical-Aperture Femtosecond Two-Photon Absorption on (SU-8) Resist for Ultrahigh-Aspect-Ratio Microstereolithography

In this paper, we systematically report the characterization and analysis on the solidification of SU-8, a chemically amplified near-UV ultra-thick resist, based on two-photon-absorbed (TPA) near-infrared photopolymerization. The resolution of TPA photopolymerized SU-8 voxels and lines was studied as a function of laser pulse energy, single-shot exposure time and scanning speed. Two-photon three-dimensional (3D) litho­graphy using SU-8 as the matrix material was verified by the fabrication of SU-8 photoplastic structures with sub-diffraction-limit resolution. We show that the non-linear velocity dependence of TPA photopolymerization can be used as the shutter mechanism for disruptive 3D lithography. This mechanism, when combined with low numerical aperture optics is exploited for the rapid microfabrication of ultra high aspect-ratio (up to 50:1) photoplastic pillars, planes and cage structures.