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Three photons make tiny shapes

12 Dec 2005

The first three-dimensional structures to be fabricated by three-photon polymerization are unveiled.

Scientists in Greece believe they are the first to fabricate three-dimensional structures by three-photon polymerization (3PP). Having produced components with a resolution of 500 nm, Maria Farsari and her colleagues from FORTH in Crete are now improving their optical setup and hope to build practical devices using the approach. (Optics Letters 30 3180)

Two-photon polymerization has been widely reported using Ti:Sapphire lasers emitting around 800 nm to create structures with resolutions of 200 nm or less. Knowing that a three-photon approach could potentially lead to better resolution, the Greek researchers developed a proof-of-principle system to see if the idea was practical.

The 3PP setup uses a compact diode-pumped femtosecond laser oscillator emitting 1028 nm, 200 fs pulses at a repetition rate of 50 MHz. An x-y galvanometric scanner equipped with a high numerical aperture objective lens focuses and translates the beam across the photopolymer at 0.75 mm/s.

Farsari and colleagues George Filippidis and Costas Fotakis used a UV photocurable organic-inorganic hybrid material known as ORMOCER. When the pulses are focused into the ORMOCER, the polymerization process is initiated by nonlinear absorption within the focal volume.

The team fabricated test structures layer-by-layer from the bottom up. Using an 1.25 numerical aperture (NA) objective lens resulted in a beam waist and a corresponding resolution of 500 nm.

"We have now replaced our 1.25 NA microscope objective with a 1.4 NA one," Farsari told Optics.org. "This should give us a resolution of 340 nm. We do not intend to join the resolution race though. Our purpose is to build functional devices using 3PP."

Farsari says the team is now concentrating on two aspects. "Firstly we are trying to dope the photopolymers with active molecules and secondly we are trying to selectively attach active molecules to the surface of the devices," she said.

Jacqueline Hewett is technology editor on Optics.org and Opto & Laser Europe magazine.

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