Micro-lens arrays generated by UV laser irradiation of doped PMMA

Micro-lenses with well-defined optical parameters are generated on polymeth ylmethacrylate (PMMA) substrates doped with diphenyltriazene (DPT) by contr olled use of a swelling effect generated under conditions of subablative ex cimer laser illumination. The surface profiles depend on the laser spot siz e and energy density. A sensitively balanced combination of matrix softenin g, substrate volume expansion due to photochemical nitrogen release, and su rface tension is responsible for the final shape of the lenses. Complete ar rays of identical lenses with 15 mu m diameters and a focal length of 30 mu m are produced by irradiation of (0.25 wt. %) DPT-PMMA with a single laser pulse at a wavelength of 308 nm and a fluence of 3J/cm(2) It is shown expe rimentally and theoretically that appropriate volume expansion is possible without introducing internal light scattering due to the formation of small bubbles.