arrays with an equal number of spots but different spot separations. The observed differences clearly illustrate the influence of the spot separation: small spacing increases the inhomogeneity even with short exposure times. Thus, it is not possible to achieve homogeneous polymerization of each voxel structure using an 11×11 spot DOE with an inter-spot distance of 0.62 µm whereas the analogue structure is easily obtained with an 11×11 spot DOE with a three times greater inter-spot distance (1.85 µm). Note that the array of voxel structures with the 0.62 µm spacing observed in Fig. , was obtained with hundred-times shorter exposure time compared to that used for the fabrication with the 1.85 µm spaced DOE. The central overpolymerization observed with the closely spaced spots is accompanied by an underpolymerization of the peripheral structures, so that some of the voxel structures in the last two rows were washed away during the development step. This behaviour supports the hypothesis that the proximity of the spots during simultaneous exposure contributes to reducing the overall polymerization threshold of each structure written in parallel, all the more so as we move closer to the center of the structure array. At small write spot spacings, this results in a non-uniform spatial profile of the polymerization threshold and a decrease of each threshold compared to sequential single-beam writing .