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IT COULD be the world’s smallest fence: a chain of five crude, squarish links is strung between posts just 40 micrometres apart. This microscopic barrier marks the threshold of a new world of fabrication.

The interlocking links of the chain would be impossible to make using conventional microfabrication techniques. Instead, they were conjured into existence by waving a magic wand – or rather, a laser beam. This method, called two-photon 3D microfabrication, is just starting to make its mark. Fast, cheap and flexible, it can create multilayered microchips, custom-designed crystals, pre-assembled propellers – tiny objects with fantastical curves, interlocking parts and 3D structures, all qualities difficult or impossible to achieve with traditional techniques. “It’s like making Frank Gehry-type buildings instead of flat warehouses,” says Malvin Teich, an engineer at Boston University.

The “flat warehouses” he means are the silicon computer chips made by photolithography, today’s standard in microfabrication. Photolithography etches the circuit onto the silicon by shining ultraviolet light through a flat mask perforated with the pattern of the chip circuitry. The technique can produce multilayer constructions, by depositing successive layers of silicon and using different masks to etch each layer, slowly building up a 3D structure. But you could never build a curvy Bilbao Guggenheim in this way.

Two-photon microfabrication is a different story. “You could do this on top of a desk, if you had the right lasers,” says John Fourkas, Teich’s collaborator at the University of Maryland in College Park. In fact, Fourkas is pretty much describing his lab, which is essentially just a big table with a laser hooked up to a computer and a few lenses. The laser scans through a drop of…