Two-step absorption instead of two-photon absorption in 3D laser nanoprinting

Two-photon absorption (TPA) 3D laser nanoprinting typically requires femtosecond lasers, which are expensive and bulky. Here, we introduce two-step absorption (TSA) replacing TPA as the nonlinear excitation mechanism. In TSA, the virtual intermediate state in TPA is replaced by a real electronic intermediate state, allowing to use inexpensive continuous-wave lasers. Concerning degenerate TSA, we demonstrate scanning single-focus nanoprinting of state-of-the-art 3D woodpiles with rod spacings down to 300 nm and below, using about 45 µW power from a compact 405 nm semiconductor laser diode. Concerning non-degenerate TSA, we present the status of our work on light-sheet 3D laser projection printing.