Fabrication of a reusable microlens array for laser-based structuring

A microlens array optic was fabricated for laser surface microstructuring of polymer surfaces. The optic contains a hexagonal close-packed monolayer of SiO₂ microspheres, held together by an adhesive substance and supported on fused silica glass. The array is placed in direct contact with the target substrate and is exposed to UV light at a wavelength of 193 nm. During this exposure, the SiO₂ spheres act as microlenses, which focus the incoming laser light, but also enhance the optical near-field intensity underneath each microsphere. A large number of identical structures are produced simultaneously using this type of direct laser ablation, which leads to a highly efficient process. The ablated holes are approximately 1.8 μm in diameter, with a pitch of 8.4 μm and a depth of 80 nm. This microlens array has many advantages over other types of array, including the fact that it is inexpensive and easy to fabricate. An important feature is that it can transmit light at a wavelength less than 300 nm, which makes it suitable for laser surface patterning.