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K. Cicha, Z. Li, A. Mautner, K. Stadlmann, J. Torgersen, N.U Pucher, R. Markut-Kohl, R. Liska, J. Stampfl:
"Fabrication and evaluation of 3D-micro-structures produced using two-photon-induced photopolymerization (TPIP or 2PP) by means of optical assessment and FTIR-spectroscopy";
Talk: Euromat 2011, Montpellier, France; 09-12-2011 - 09-15-2011; in: "Conference Proceeding Euromat 2011", (2011), 0453.

Two-Photon Polymerization (2PP) has recently gained a lot of interest as additive manufacturing technology capable of fabricating complex 3D submicron structures. Parts produced with this technology can be used in various future applications e.g. mechanical, electronic and optical micro devices. This paper presents achievements in the fabrication of 3D-micrometer-structures as well as a two methods and procedures for evaluating photopolymers in terms of their usability or 2PP.
The structuring was performed employing a pulsed near infrared Ti:Sapphire femtosecond laser with a pulse-width of less than 100fs, a repetition rate of 80MHz and a wavelength of 793nm. In combination with a 100x magnification microscope (NA 1.4) the maximum laser-power is 145mW.
For material research a reliable evaluation system is indispensable to compare different materials. Due to the small sample size and long fabrication-times (typical feedrates are between 100μm/s and 1mm/s) traditional material testing methods (e.g. tensile test,
notch-bar impact test, etc.) cannot be used for 2PP-structures. Therefore more applicable methods had to be developed to provide a
solid base for investigations on the 2PP process.
The first developed method works by optical assessment. Therefore an evaluation system containing 4 classes was established and different material compositions were tested and compared for their applicability for 2PP. This method allows a fast screening of the
samples, but relies on the subjective view of the evaluator. Therefore a more quantifiable method was established. The double-bond conversion (DBC) was measured by means of IR-spectroscopy using a FTIR spectrometer connected to an IR spectroscopy microscope. The change of the double-bond peak gives direct information about the double-bond conversion. Several problems like sample preparation, sample handling and fabrication of the 2PP full-solid box-like structures had to be solved. An array of photonic crystals with different laser intensities and writing speeds was fabricated on a potassium bromide plate. A high influence of the laser power was observed; the feedrate influenced the DBC only at low laser powers levels. Further investigations are necessary to determine all relevant parameters for a better and comprehensive understanding of the 2PP process.
Additionally, fabrication of complex 3D-structures started to determine the limits of the 2PP technology for miscellaneous components.

Two-photon-polymerization, material characterization, FTIR-spectroscopy, micro-structure

http://publik.tuwien.ac.at/files/PubDat_201028.pdf

Project Head Jürgen Stampfl:
ISOTEC III - Integrated Organic Sensor and Optoelectronic Technologies (Phase 3)