Plasma Meets Glass

Abstract

Due to its particular optical and mechanical properties, fused silica is one of the most relevant materials for the production of optical, opto-mechanical and opto-electrical components and systems. Since such glasses feature a high transmittance in the ultraviolet (UV) spectral range, deep UV-laser irradiation or several hybrid methods are usually applied in laser-based manufacturing of optically operative micro-structures on fused silica substrates. Against this background, the development of novel methods for increasing the UV-absorption temporarily is of great interest for laser scribing of optical gratings, micro optics and integrated optical systems. Here, cost-and energy-efficient plasma treatment techniques at atmospheric pressure offer different approaches that can also be applied to other optical glasses.For enhancing the energy deposition into glass substrate surfaces during laser micro structuring, several techniques are in hand. For example, the application of carbon-based thin films allows increasing the absorption of glasses in the UV-range [1]. Further, UV-absorbent silicon suboxide (SiO x ) can be applied by vacuum deposition and micro structured subsequently. Finally, such structured suboxide layers are oxidised to silicon dioxide (SiO 2 ) [2]. The use of hydrogenous gases at high temperatures also allows a direct modification of near-surface SiO 2 bulk material to SiO x [3]. In this contribution, the generation of silicon suboxide in the near-surface region of fused silica bulk material by introducing a plasma treatment at atmospheric pressure and ambient temperature as well as related effects are presented. Although a plasmainduced chemical modification is strongly dependent on the chemical composition of the particular glass, this method also allows altering near-surface properties of multi component glasses such as crown or flint glasses. Further, several plasma-based methods for enhancing laser ablation of glasses are described. In this context, the influence of the use of inert argon as process gas on the treatment and hybrid ablation of optical glasses is discussed. The plasma modification processAtmospheric pressure plasma (APP) induced modification of fused silica can be achieved by the use of different APP-sources, using forming gas 90/10, a mixture of nitrogen N 2 (90 %) and hydrogen H 2 (10 %), as process gas. By dissociation and ionisation processes, excited and reactive species of N and H are generated within the plasma volume when realising a plasma power density in the range of some tens of mW/mm². As shown by the schematic functional principle in Figure 1, such species can effect a reduction of SiO 2 to oxygen-depleted SiO x by different chemical reactions. CHriSToPH GerHArDGerhard studied precision production engineering in Göttingen and Paris and subsequently worked as product manager for optics and university lecturer in Göttingen. During his following occupation as research associate in Bremen, he extra-occupationally studied Optical Engineering/Photonics. He now works as r...

Plasma-Induced Generation of Optically Active Defects in Glasses

“…the imaginary part of the complex index of refraction, respectively. Consequently, the index of refraction n, which is the real part of the complex index of refraction, increases as well as ascertained via ellipsometric and interferometric measurements [16], see Fig. 5.…”