Three-dimensional microfabrication by femtosecond pulses in dielectrics

We report femtosecond laser microfabrication in thin films of polymeric photoresists by (i) direct laser writing and (ii) holographic recording techniques. With (i) we have fabricated empty microchannels in polymethylmethacrylate; the channel width closely follows the intensity distribution in the focal spot of a high numerical aperture lens in accordance with scalar and vectorial Debye theory. With (ii) we have fabricated free-standing two-dimensional periodic structures in SU8 photoresist. The structures contain cylindrical pillars with noticeable ripple-like modulation of their diameter along their axes. This modulation results from the interference between the waves incident on the sample and back-reflected from the glass substrate or air, and is explained using an appropriate numerical modeling. (C) 2003 Elsevier B.V. All rights reserved.