Two-step absorption instead of two-photon absorption in 3D nanoprinting
V. Hahn, T. Messer, N.M. Bojanowski, E.R. Curticean, I. Wacker, R.R. Schröder, E. Blasco, and M. Wegener
Nat. Photonics 15, 932-938 (2021)
- Date: 29.11.2021
The quadratic optical nonlinearity arising from two-photon absorption provides the crucial spatial concentration of optical excitation in three-dimensional (3D) laser nanoprinting, with widespread applications in technical and life sciences. Femtosecond lasers allow for obtaining efficient two-photon absorption but are accompanied by a number of issues, including higher-order processes, cost, reliability and size. Here we introduce two-step absorption replacing two-photon absorption as the primary optical excitation process. Under suitable conditions, two-step absorption shows the same quadratic optical nonlinearity as two-photon absorption. We present a photoresist system based on a photoinitiator supporting two-step absorption, a scavenger and a well-established triacrylate. We show that this system allows for printing state-of-the-art 3D nanostructures and beyond. In these experiments, we use ~100 μW optical power from an inexpensive, compact continuous-wave semiconductor laser diode emitting at 405 nm wavelength. Our work opens the door to drastic miniaturization and cost reduction of 3D laser nanoprinters.
P.V. Braun and M.L. Brongersma, "Photochemistry democratizes 3D nanoprinting" in Views & News; Nat. Photonics 15, 871-873 (2021)