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.

由双光子吸收引起的二次光学非线性提供了三维 (3D) 激光纳米打印中光激发的关键空间集中，在技术和生命科学中具有广泛的应用。飞秒激光器允许获得有效的双光子吸收，但伴随着许多问题，包括高阶工艺、成本、可靠性和尺寸。在这里，我们介绍两步吸收代替双光子吸收作为主要的光学激发过程。在合适的条件下，两步吸收显示出与双光子吸收相同的二次光学非线性。我们提出了一种基于支持两步吸收的光引发剂、清除剂和成熟的三丙烯酸酯的光刻胶系统。我们表明，该系统允许打印最先进的 3D 纳米结构及其他结构。在这些实验中，我们使用来自廉价、紧凑的连续波半导体激光二极管的约 100 μW 光功率，发射波长为 405 nm。我们的工作为 3D 激光纳米打印机的大幅小型化和降低成本打开了大门。