Abstract
A Cyclo Olefin Polymer (COP), Zeonex® glass exhibits advantage for applications in photonics: high transparency from NIR to UVA, humidity insensitivity and refractive index stability. We thus studied this organic glass, made with only carbon and hydrogen to show that it can be used as a substrate for photonics. We investigated the microscale transformations induced by fs laser direct writing according to parameters: pulse energy, repetition rate, scanning speed (or time of irradiation). We pointed out two domains of modifications, one at low mean power between 0.1 and 20 mW and another above 20 mW. We called them type I and II. In type I, two basic modifications – photoluminescence (PL) creation are restricted to the irradiated volume at the scale of beam size, a large refractive index change (+0.14) appears when the pulse repetition rate is high(>500 kHz), enabling local modulation of optical properties for potential applications. Here, modification of the COP molecule is moderate and the spatial sensitivity is of the order of μm. In type II, the modification is more extended but PL is much stronger. Through correlations between the PL results, we defined signatures composed of luminophore series: S1 associated to type I, S2 associated to type II and S3 for intermediate conditions. S1 is the luminescent group, with the largest yield excitable at 475 nm with a broad emission from green to orange-yellow. S2 is remarkable with a broad excitation in the green and broad emission in yellow range. S1 and S3 results from small molecular modification but S2 is likely resulting from the disruption of COP molecule forming Carbon Dots.
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