From Guy Cox, Sydney, New South Wales, Australia
Two readers pointed out that back in 1974, New Scientist columnist Daedalus proposed 3D printing by laser beam polymerisation within a liquid resin – rather than accreting layers as in modern 3D printing (Letters, 12 November). Something similar has actually been done by Satoshi Kawata and colleagues at Osaka University, Japan. Their masterpiece, created in 2001, was a complex sculpture of a prancing bull – the size of a red blood cell (18 August 2001, p 7).
Rather than using two laser beams as Daedalus proposed, they used one pulsed beam. They depended on the fact that in two-photon reactions both must hit the molecule simultaneously, which will only happen at the centre of the focused spot.
