UV direct laser interference patterning of diffraction gratings in poly-hydroxyethyl-methacrylate ophthalmic polymers
Laser-induced refractive index modification by using micro-structuration of diffractive optical devices in ophthalmic polymers is of great interest in the fields of Optics and Ophthalmology. In this work, poly-hydroxyethyl-methacrylate, PHEMA, polymers used as soft contact lenses were structured with linear periodic patterns by means of Direct Laser Interference Patterning, DLIP. Periodic modulation on the surface of the polymer material was attained under two-beam interference with a Q-switched laser source with emission at 266 nm and 10 ns pulse duration. Features of the laser processed areas were studied as a function of both the laser fluence and the interference period. Topography of structured areas was investigated using optical confocal microscopy. Compositional and structural modifications of the processed material were studied by means of micro-Raman spectroscopy, and scanning electron microscopy, SEM, confirming that at low laser fluences structured material remained unaltered. Finally, both diffractive properties and refractive index modification were assessed through diffractive techniques under illumination of a continuous-wave 632.8 nm He-Ne laser resulting in values ranging 7.8×10-2 and 5.6×10-2.