Localized Polymerization Using Single Photon Photoinitiators in Two-photon process for Fabricating Subwavelength Structures

Abstract: Localized polymerization in subwavelength volumes using two photon dyes has now become a well-established method for fabrication of subwavelength structures. Unfortunately, the two photon absorption dyes used in such process are not only expensive but also proprietary. LTPO-L is an inexpensive, easily available single photon photoinitiator and has been used extensively for single photon absorption of UV light for polymerization. These polymerization volumes however are not localized and extend to micron size resolution having limited applications. We have exploited high quantum yield of radicals of LTPO-Lfor absorption of two photons to achieve localized polymerization in subwavelength volumes, much below the diffraction limit. Critical concentration (10wt%) of LTPO-Lin acrylate (Sartomer) was found optimal to achieve subwavelength localized polymerization and has been demonstrated by fabricating 2D/3D complex nanostructures and functional devices such as variable polymeric gratings with nanoscaled subwavelength resolution. Systematic studies on influence of LTPO-L concentration on two photon polymerization of commercially available photopolymer (Sartomer) show that resolution of the fabricated structures critically depend on loading of LPTO-L. This is expected to unleash the true potential of two photon polymerization for fabrication of complex polymeric nanodevices at a larger scale.