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3 September 2008 Exceeding the diffraction limit with single-photon photopolymerization and photo-induced termination
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The fabrication of 3D microstructures has been realized by numerous researchers using two-photon polymerization. The premise of these studies is that the confinement provided by localized, two-photon absorption results in polymerization only near the focal point of the focused write beam and unwanted polymerization due to superposition of the out-offocus exposures is significantly reduced, enabling the fabrication of complex structures with features below the diffraction limit. However, the low cross-section of two-photon absorbers typically requires excitation by pulsed Ti:Sapphire laser at 800 nm, resulting in polymerized features that are actually larger than those created by one-photon absorption at half the wavelength. Here we describe a single photon photolithographic technique capable of producing features not limited by the physics of diffraction by utilizing a resin which is able to be simultaneously photoinitiated using one wavelength of light and photoinhibited using a second wavelength. Appropriate overlapping of these two wavelengths produces feature sizes smaller than the diffraction limit and reduces polymerization in the out-of-focus regions while avoiding the high light intensities demanded by multi-photon initiation. Additionally, because the photoinhibiting species are non-propagating radicals which recombine when the irradiation is ceased, memory effects typical of photochromic initiators are avoided, allowing rapid and arbitrary patterning.
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Benjamin A. Kowalski, Timothy F. Scott, Christopher N. Bowman, Amy C. Sullivan, and Robert R. McLeod "Exceeding the diffraction limit with single-photon photopolymerization and photo-induced termination", Proc. SPIE 7053, Organic 3D Photonics Materials and Devices II, 70530E (3 September 2008);

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