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Sub-micron-period surface gratings on Ta O waveguide layers were produced by ablation with a sub-ps-UV-laser. The 2 5 structure is generated by projection imaging of a primary transmission grating mask. A grating of 500 nm period with a surface modulation depth of 10 nm on a sample area of about 300 mm = 300 mm can be produced with a single laser pulse of about 100 mJrcm 2 at 248 nm. Adjustment of the modulation depth to specific requirements can be accomplished by varying laser fluence or pulse number. The structures can be used as grating couplers. q 1999 Elsevier Science B.V. All rights reserved.

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The micromachining of composite materials using excimer lasers has not yet been the subject of in depth investigations. In this work the authors studied the ablation behavior of Al 2 O 3 -34 wt % TiC composite ceramic using 500 fs laser pulses at 248 nm. It was found that the roughness does not change significantly with the number of pulses for constant laser fluences. The ablation rate decreases with increasing number of pulses reaching a stationary regime after 100 pulses. Characterization of the machined areas by scanning electron microscopy showed that a globular topography is responsible for the roughness of the samples. Increasing the laser fluence up to 12 J/cm 2 increases the ablation rate for a constant number of pulses and decreases the surface roughness. At this fluence the measured roughness R a was around 0.1 m, when the original surface had a R a Ϸ0.05 m. Chemical changes of the irradiated surface were investigated using Auger electron spectroscopy. Based on these results ablation mechanisms are suggested. Machining of submicron structures on the material is presented. Periodic line structures with line spacing below 520 nm were produced on the surface by multiple laser shot exposure. By using such structures one can identify different ablation thresholds for the constituents of the ceramic composite. Atomic force microscopy was used to characterize the surface topography.

Nanostructure / Laser Ablation / uv-Femtosecond Laser / WaveguideWe report on the fabrication of periodic nanostructures on selected materials by shortpulse uv-laser ablation. Temporal studies reveal details of the ablation process with subpicosecond time resolution. Biochemical applications of the nanostructures for planar waveguide technology are presented.