Microfabrication by femtosecond laser irradiation

Femtosecond (fs) laser microfabrication has been gathering more research interests due to its ability to create micro- and sub-micrometer three-dimensional (3D) structures. An extremely high light intensity (approximately TW/cm²) enables multiphoton absorption (MPA) in transparent materials, upon which the spatial resolution of fabricated elements is confined to the sizes even smaller than optical diffraction limit. Our report will formulate the principles of the laser microfabrication of such applications. A direct application of single-shot pulse-induced optical damage is a 3D optical memory with a storage density of ca. 100 Gbits/cm² in silica. Photonic and optoelectronic applications such as optical gratings, 3D inlayed-`atom'-like and 2D cylinder-consisted photonic crystals have been fabricated in silica. Also, photopolymerization of photoresist by a scanning of focal point of laser irradiation solidifies submicrometer rods, which forms photonic lattices when packed into well-defined 3D pattern. Photonic bandgap effects (at 2-4 μm) of above-mentioned structures were corroborated by infrared Fourier spectroscopy and numerical simulations, by which the success of laser microfabrication was evidenced. Self-focusing of fs-pulses (optical Kerr effect) is another possibility of the microstructuring of transparent materials, which is demonstrated in the case of silica. This could find its application in sub-diffraction-limited recording.