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Two photons aid precise lithography

27 Feb 2004

A blend of two-photon absorption and organic dyes mixed in a resin generates 3D structures with sub-micrometer precision.

Shining lasers onto a resin slab that contains special organic dyes can produce 3D structures with sub-micrometer precision, according to researchers at Georgia Institute of Technology, US.

The team says that the technique, known as two-photon 3D lithography, could provide a new way to make devices such as photonic bandgap structures, optical storage devices, photonic switches, sensors, micromachines and scaffolds for growing living tissue.

Two-photon 3D lithography exploits the properties of a particular family of organic dyes developed at Georgia Institute of Technology. The dyes, bis-donor phenylene vinylenes, can absorb two photons simultaneously and this excitation can initiate chemical reactions such as polymerization.

The technique involves adding a small concentration (0.1%) of the dyes into a resin slab along with an acrylate monomer that can be cross-linked. When a focused near-infrared laser beam is shone onto the slab, the dye molecules near the beam’s focus are excited, which causes the monomers to polymerize.

The resulting polymer is insoluble while the unilluminated monomer is still soluble. This means that the parts of the slab that have not been exposed to the light can be washed away, leaving a complex 3D structure. The researchers have used this method to make a variety of structures, including objects with moving parts like gears and chains.

According to the team, the technique can write 3D patterns in polymer slabs that are 100 microns thick, at light intensities low enough to avoid damaging the materials. A key feature of the technique is that it only works when two photons are absorbed. As the probability of this happening drops off rapidly with distance from the laser's focal point, the patterning is very precise. "Using 700 nm light, the patterning precision can be about 200 nm across by 800 nm in depth," explained team member Seth Marder.

The researchers described their technique at the annual meeting of the American Association for the Advancement of Science (AAAS), held earlier this month in Seattle, US. The technology has now been licensed to a company called Focal Point Microsystems, which Marder and his fellow researcher, Joseph Perry helped to set up.

Siân Harris is features editor of Opto & Laser Europe magazine.

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