Applications of cold atmospheric pressure plasmas in optics manufacturing

Finishing of optical components is one of the main challenging tasks in optics manufacturing. This includes precision polishing, smoothing, and surface modification, e.g. for subsequent contact bonding. Recent developments have shown that the use of dielectric barrier discharge plasmas at atmospheric pressure allows for the conception and realization of novel approaches for such surface finishing. Since this type of plasma stands out due a low gas temperature, it is also referred to as “cold” plasma. It is thus suitable for the treatment of temperature-sensitive optical media. In this contribution, selected applications of such plasmas in optics manufacturing are presented. First, it is shown that precision polishing of different optical media can be achieved by the use of direct plasma discharges with an inert process gas. By the plasma-induced selective removal of roughness peaks, a notable decrease in surface roughness of the initial value was obtained. Second, plasma-induced cleaning of optics surfaces including the underlying plasma-physical and plasmachemical mechanisms is presented. Here, not only surface-adherent carbonaceous contaminations, but also residues from polishing agents and other operating materials can be removed. Such cleaning results in several advantageous effects as for example an increase in laser-induced damage threshold or a modification in free surface energy, leading to an improved adhesion of coatings and cements. Finally, plasma treatment is suitable for refractive index matching of glass surfaces by a plasma-induced modification of the chemical composition of the near-surface glass layer.