  Light-matter interactions in the deep ultraviolet (DUV) wavelength region
exhibits a variety of optical effects such as luminescence, photoisomerization,
and polymerization in many materials. Despite the rich photochemistry and high
spatial resolution due to the short wavelength, the notorious lack of
DUV-compatible optical components and devices precludes use of DUV light in
microscopy and lithography as a routine laboratory tool. Here, we present the
use of two-photon excitation with visible laser light to realizes
photo-polymerization of molecules with an excitation energy equivalent to DUV
light. Using standard optics for visible light, methacrylate oligomers were
polymerized with 400 nm femtosecond pulses without any addition of
photo-initiators and sensitizers. By scanning the laser focus in 3D, a series
of fine 3D structures were created with the smallest resolved line-space
features of 80 nm. We found DUV polymerizations induced by two-photon
absorption is surprisingly efficient and requires laser intensity only on the
order of 100 kW/cm^2. With the variety of successful demonstrations including
organic- and inorganic-material-made-structures presented, our direct
nano-3D-printing method would be a valuable tool for nanofabrication in 3D.
