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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.
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