In this contribution, we present a plasma-based approach for modifying the focal length of plano-convex lenses realised by the deposition of droplets made of optical cement. For this purpose, PMMA and soda-lime glass substrates were treated with a direct dielectric barrier discharge plasma at low pressure. To obtain plasma-induced changes in surface energy of the substrates by the formation of functional groups, octafluorocyclobutane (C4F8) was used as process gas. Such treatment lead to a notable decrease in surface energy and especially its polar fraction, which is attributed to the generation of fluorocarbon compounds such as polytetrafluoroethylene (PTFE) as also confirmed by FTIR spectroscopic measurements. It is shown that this effect has a considerable impact on the contact angle and radius of curvature, respectively, of the deposited cement droplets where differences by a factor of about two were obtained. After curing of the cement, front focal lengths in the range from approx. 5 to 13 mm were realised depending on the duration of the plasma pre-treatment. The cement lenses finally feature dimensions in the range of some millimetres.

中文翻译：

---

C4F8 等离子体处理用于改变不同基材上液基平凸透镜的焦距

在这篇文章中，我们提出了一种基于等离子体的方法，用于修改由光学胶粘剂制成的液滴沉积实现的平凸透镜的焦距。为此，在低压下用直接介质阻挡放电等离子体处理 PMMA 和钠钙玻璃基板。为了通过形成官能团来获得等离子体引起的基材表面能变化，使用八氟环丁烷 (C4F8) 作为工艺气体。这种处理导致表面能，尤其是其极性分数的显着降低，这归因于碳氟化合物如聚四氟乙烯 (PTFE) 的产生，这也由 FTIR 光谱测量证实。结果表明，这种效应分别对接触角和曲率半径有相当大的影响，沉积的水泥滴，其中获得了大约两倍的差异。水泥固化后，前焦距范围约为 根据等离子体预处理的持续时间，实现了 5 到 13 毫米。水泥透镜最终具有几毫米范围内的尺寸。