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Conference: Bucharest University Faculty of Physics 2008 Meeting

Section: Optics, Spectroscopy, Plasma and Lasers

Title:

3D Geometry Created by DLW in Polymers using Femtosecond Laser Pulses

Authors:

Florin JIPA, Iulia ANGHEL, Marian ZAMFIRESCU, Razvan DABU

Affiliation:

National Institute for Laser Plasma and Radiation Physics - INFLPR , Atomistilor 409, 077125 Magurele, Bucharest, Romania

E-mail

florin.jipa @inflpr.ro

Keywords:

Abstract:

The polymers are very promising materials for creating structures such as photonic crystals, metamaterials, MEMS, with very broad application domains such as optical devices, telecommunications, medicine, etc. In this work we present the experimental setup for femtosecond laser processing of polymers and the results of laser structuring using the photopolymerisation technique. When an infrared femtosecond laser beam is tightly focalised into a material transparent to the laser radiation wavelength, due to the very high laser power density (GW-TW/cm2) nonlinear optical effects such as multiphotonic absorption can be induced in a volume smaller than the focused spot size. Therefore, irreversible physical and chemical transformation of the material can take place and structures with dimensions below the diffraction limit can be produced only where the laser intensity surpass the threshold of the nonlinear optical effect. A standard Direct Laser Writing (DLW) setup was configured and used in order to tightly focus the laser beam in the volume of the transparent polymer. Our laser processing setup is composed by a femtosecond laser in CPA configuration delivering laser pulses with energy of 0.7 mJ, time duration of 180 fsec at 775 nm wavelength and 2 kHz repetition rate. The laser can be continuously and precisely attenuated in the rage of few nJ to hundreds on nJ. The laser is focalized in the volume of the sample using a microscope objective with high numerical aperture, and magnification. The sample is translated by a computer controlled translation stage in XYZ with resolution below 100 nm. The laser focalization and the laser processing are visualized and controlled in real-time by an optical system with high resolution of about 1 m. The maximum absorption band of the photopolymers is usually centered in the UV spectral range. High energy density obtained in the focalized laser spot will induce photochemical reactions even under infrared irradiation due to the multiphoton absorption effect. When a proper processing protocol is followed, the cross-linking of the chemical species occurs in the material`s volume. By translating the photosensitive resin under the laser beam, any 3D geometry can be generated by two-photon photopolymerisation. For the studied polymers we tested their response to different laser irradiation energy density, irradiation time, and adhesion to the substrates. We established the optimum laser processing protocol in order to have good structures with submicron resolution. Different structures were created by direct laser writing technique and characterized by optical microscopy, AFM and SEM. Acknowledgments: This work was financially supported by the project PNCDI 2_ ID-PCE-268.