Fabrication and characterization of diffraction gratings in ophthalmic polymers by using UV Direct Laser Interference PatterningFriday (26.06.2020) 12:10 - 12:30 Room 2
The fabrication of diffractive elements in ophthalmic polymers to induce refractive index changes which can be applied for refractive correction is of great interest in the fields of Optics and Ophthalmology [1-5]. In this work, poly-hydroxyethyl-methacrylate (PHEMA) and silicone hydrogel polymers used as soft contact lenses were structured with linear periodic patterns by means of Direct Laser Interference Patterning (DLIP). A Q-switched laser delivering 10 ns laser pulses at 266 nm and the two-beam configuration setup were used to fabricate periodic line-like patterns with spatial periods of 2.6 µm and 4.7 µm. Optical confocal microscopy showed that at low laser fluences, the laser-matter interaction process in both polymers resulted in the swelling of the polymer surface, as shown in Figure 1(a). Furthermore, the height of the periodic structure decreased when decreasing the spatial period. Compositional and structural modifications carried out by means of micro-Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) showed that at low laser fluences the material remained almost unaltered whereas at high laser fluences the material underwent degradation with significant changes in the chemical structure. Finally, diffraction assessment carried out under illumination of a continuous-wave 632.8 nm He-Ne laser in the DLIP processed areas showed diffraction patterns at both spatial periods, 4.7 µm and 2.6 µm, as shown in Figure 1(b) . First- and second-order efficiency augmented with the laser fluence increase. Refractive index change induced by the laser processing resulted in values between 5.3×10-2 and 8.5×10-2, which were similar to those reported by using the Ultrafast Laser Inscription (ULI) technique but with an improvement of the processing yield of more than two orders of magnitude [1, 2].
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