Design and characterization of harmonic diffractive microlens arrays with continuous relief for parallel laser direct writing

To make the real-time focusing possible in the exposure process, diffractive microlens arrays with continuous relief are designed and fabricated using harmonic diffraction theory for parallel laser direct writing to integrate the exposing and autofocusing functions in one array by taking both the writing resolution and diffraction efficiency into consideration. A theoretical model is established using Rayleigh-Sommerfeld diffraction theory to accurately characterize the focusing characteristics of each harmonic diffractive microlens in the array so that the fidelity of pattern can be improved through exposure dose modulation. The measurements made indicate that the experimental results coincide well with the theoretical results when the writing laser with a wavelength of 441.6nm and the autofocusing laser with a wavelength of 670 nm are normally incident on an array with an F-number of F/4 fabricated on fused silica, and the array developed can be used to synchronously focus the writing laser and the autofocusing laser into the same spot of the array. (C) 2009 Elsevier Ltd. All rights reserved.