Bright IDEAS Award: Nanoparticles On demand Via multiphoton Absorption (NOVA): the practical nanoparticle-making machine.

制造纳米颗粒和打印纳米尺寸的材料是当今重要的研究课题。然而从材料制造的角度来看，显而易见的问题是如何制造纳米级物体，如何优化它们的尺寸和尺寸分布，它们的精确形状等等，所需要的是一种加工技术，可以从起始前体液体或气体生成纳米级材料。利用高功率脉冲激光源的多光子吸收过程，这种技术现在应该是可能的。当一个高峰功率的激光源被聚焦到一个小的光斑尺寸时，就会发生多光子吸收，从而产生一个高得令人难以置信的局部光子密度。在聚焦区域内，液体或气体等在基本激光波长下不吸收的材料现在可以通过一次吸收几个光子来吸收。如果你使用多个激光源，都聚焦到同样小的光斑尺寸，并使焦点区域重叠，那么吸收将只发生在这个微小的相互作用体积内，一个3d像素或体素。然后，液体或气体可以分解，将金属等元素释放到基本上“自由空间”中。多光子吸收依赖于激光源的局部亮度（每单位时间的光子密度），因此该技术应允许在极小体积内合成材料，特别是远小于入射激光的波长。正是在这个体素中，你想要的纳米粒子诞生了。改变参数，如激光束重叠，激光波长或输入光偏振产生一个非常多功能的工具箱，用于纳米粒子的产生。球形、椭圆形、空心、弦或弹簧，许多这样的形状应该是可能的。如果两种不同的材料同时流过相互作用区域，可以制备纳米合金、涂层纳米颗粒等。如果前体材料流过基底，那么通过多光子吸收的局部分解将导致打印金属、半导体等材料的小点和线。这是该计划的第二部分，其目的是遵循制造“自由”纳米粒子以及打印纳米级物体的两条路线。到目前为止，还没有人尝试过用3d多光子技术来制造材料。许多团体已经成功地通过单光束，多光子技术，例如在液体单体中写入结构，并制作了异国情调的微型雕塑，如公牛，雕像和蜘蛛，但只有聚合物。如果成功的话，这种全新的多光束方法将带来可控的纳米颗粒，以及3d纳米雕刻，无论你能从原始液体或气体前体的分解中生产出什么材料。

Making nanoparticles, and printing of materials with nanoscale sizes is an important research topic these days. From a materials manufacturing point of view however, the obvious questions are how to make nanoscale objects, how to optimize their size and size distribution, their exact shape and so on. What is needed is a processing technique that will allow nanoscale materials to be generated from starting precursor liquids or gases. Using the process of multiphoton absorption of high power pulsed laser sources, such a technique should now be possible. Multiphoton absorption occurs when a high peak power laser source is focused down to a small spot size, producing a local photon density that can be incredibly high. Within the focal region, materials such as liquids or a gas that do not absorb at the fundamental laser wavelength can now do so by absorbing several photons at once. If you use multiple laser sources, all focused down to equally small spot sizes, and make the focal regions overlap, then absorption will occur only within this tiny interaction volume, a 3-d pixel or voxel. The liquid or gas can then decompose, releasing elements such as metals into essentially 'free space'. Multiphoton absorption relies on local brightness (photon density per unit time) of the laser sources, and so the technique should allow materials synthesis within extremely small volumes, and specifically much smaller than the wavelength of the incident laser light. It is within this voxel that the nanoparticles you want are born. Changing parameters such as laser beam overlap, the laser wavelength, or input light polarization generates a fantastically versatile toolbox for nanoparticle generation. Spherical, ellipsoid, hollow, strings or springs, many such shapes should be possible. If you simultaneously flow two different materials through the interaction region, you can make nano-alloys, coated nanoparticles, and more.If the precursor materials flow over a substrate, then local decomposition via multiphoton absorption will lead to the printing of small dots and lines of materials such as metals, semiconductors and more. This is the second part of the programme, and the intention is to follow both routes of making 'free' nanoparticles as well as printing of nanoscale objects. Nobody has so far attempted this 3-d multiphoton route to materials manufacturing. Many groups have successfully written structures via single beam, multiphoton techniques, in liquid monomers for example, and have produced exotic miniature sculptures such as bulls, statues and spiders, but only in polymers. If successful, this radically new multi-beam approach will lead to controllable nanoparticles on demand, and 3-d nano-sculpting in whatever material you can produce from decomposition of the original liquid or gas precursor.