Improvement of the optical and morphological properties of microlens arrays fabricated by laser using a sol-gel coating

We present a simple, repeatable and non-contaminant method to improve the optical and morphological properties of microlens arrays. It consists on depositing hybrid SiO ₂ (TEOS, MTES) coatings via sol-gel route onto microlens arrays fabricated using a Ti:Sapphire Femtosecond Amplitude Systems S-pulse HP laser operating at 1030 nm. The deposited silica sol-gel layer reduces the surface roughness (quantified as the root mean square) and increases the quality of the interstices between the microlenses generated by the ablation process, thus improving the contrast and homogeneity of the foci of the microlens array. The proposed technique allows us to obtain microlenses with a diameter in the range of 15-20 μm and a depth of 1.5-15 μm. For the characterization of the micro-optical structures, the UV-visible spectroscopy, spectral ellipsometry, confocal microscopy and beam profilometry were used. The proof-of-principle presented in this paper can be used to improve the optical and morphological properties of micro-optical systems of different nature by tailoring the parameters involved in both the laser ablation and sol-gel processes comprising the starting materials, solvent and catalysts nature and concentration, hydrolysis ratio, aging time and/or deposition conditions.