3D/4D Two-Photon and Two-Step Laser Nanoprinting—Recent Progress

We review recent progress of our group, emphasizing the following two aspects. (i) Using two-photon absorption and a dedicated sample cell, which allows to apply quasi-static electric fields with variable orientation, we are able to align the director of liquid-crystal networks in-situ during the two-photon printing process. Thereby, we can obtain nearly arbitrary distributions of the liquid-crystal director field in three dimensions. Several examples of 4D microstructures will be given. (ii) We introduce two-step absorption instead of two-photon absorption for 3D laser micro- and nanoprinting. Two-step absorption can be mediated by inexpensive compact low-power continuous-wave lasers. Degenerate two-step absorption allows for 3D laser nanoprinting by scanning a laser focus. Non-degenerate two-step absorption enables light-sheet 3D laser microprinting based on a fixed light-sheet onto which two-dimensional images are projected.