| Abstract [eng] |
Transparent materials find widespread use in well-established and emerging industries, including microelectronics, photovoltaics, optical components, and biomedical devices. Consequently, the surface functionalization of these materials represents a promising approach to customizing their properties for applications in these fields. Direct Laser Interference Patterning (DLIP) stands out as a versatile method for creating precisely defined microstructures. DLIP involves the superposition of multiple laser beams to generate an interference pattern on the surface of the material. Through precise manipulation of several parameters such as the number of interfering beams, their angle of overlap, the wavelength of the laser radiation, and the applied fluence, a diverse range of patterns, periodicities, and aspect ratios can be attained. For anti-reflection applications in the visible range, the structures have to reach values that are much smaller than the sub-micron scale (< 300 nm). Since the spatial period of the obtained patterns depends on the beam wavelength and overlapping angle, it is necessary to work at short wavelengths (e.g. UV) and increase the overlapping angle to obtain very small structures. Hence, in this work, DLIP was performed on two transparent materials, sapphire, and polycarbonate (PC), using a custom-made f-theta lens with a large aperture (d=20 mm) and a small focal length (F30mm), with the 3rd harmonic (343 nm) of femtosecond ytterbium laser. The feasibility of producing micropatterns on sapphire and PC by non-linear absorption of interfering laser beams (two beams and four beams) was demonstrated. It was also shown that using a lens with a large entrance pupil and a short focal length enabled decreasing the periodicity from 7.3 µm to 2.3 µm for the same setup. Moreover, with a higher aperture scanner, it was possible to separate the beams as much as possible and hence lower the periodicity from 5.3 µm to 1.2 µm. These structures contained holes with a diameter down to 147± 27 nm, making them suitable for anti-reflection purposes. The impact of the pulse energy, the number of passages, and the overlap of pulses on the structure were also investigated. Yet, further investigations need to be done to optimize the process and study the optical properties of the modified surfaces. |
