## 1 Introduction  
Since the realisation of the first cemented doublets in the mid-19 th century, optical cements have played a key role for the manufacture of optical systems and instruments. Nowadays, classical resins and modern UV-curable cements are used for realising a variety of bonded optical components such as aplanatic, achromatic or apochromatic lenses [1; 2; 3; 4; 5]. Further, such optical cements are used for connecting optical communications devices, i.e., fibres and waveguides [6; 7], for mounting optics [8; 9] and for photonic packaging [10]. However, a number of influencing parameters and effects can contribute to a possible failure of cemented glass bonds as summarised in [11]. These include cleaning and testing procedures, the properties and surface state of the optical components, the quality and type of cement, the environmental conditions during cementing and the cementing and curing process. For instance, it is known that inhomogeneous curing due to inhomogeneous illumination by UV-light may lead to delamination and adhesive failure as a result of shaded, non-cured areas [10]. Another reason for adhesive failure is permanent mechanical shear stress within the cement layer and at its interfacesthat arises from different indices of thermal expansion of the involved optical media [12]. Moreover, moisture and the accompanying penetration of hydrogen into cements may cause decrementing [13] and, furthermore, dissolved oxygen is known to cause failure of cement films [14]. In order to overcome the problem of delaminating cementations, different alternative techniques were developed in the past. Apart from laser welding [15; 16; 17], optical contact bonding allows the long-term connection of two optical components by contacting without any additional cement [18]. In this case, bonding occurs on the basis of pure physical and intermolecular adhesion that arises as long as the form deviation between both components is smaller than one nanometre [19; 20]. The strength of such connection can furthermore be improved by the additional application of sol gel nanoparticles [21] or the approach of activated covalent bonding where hydroxyl groups are attached on the glass surfaces prior to contacting [22; 23]. In any case, several material-specific characteristics and properties of the involved glasses and used cements have to be taken into account in order to realise a stable and long-term connection of optical components. One particular point is surface contamination, which may cause a failure of cemented bonds. Such contamination can even occur in the form of residues from operating materials used in classical optics manufacturing such as polishing or cleaning agents [24; 25]. Especially surface-adherent water or hydrogenous compounds are precursors for failure of natural cements such as Canada balsam. Against this background, tempering is applied prior to cementing [26]. Another approach for cleaning surfaces to be cemented is the use of technical plasmas. For example, this method has a number of potential applications in medicine and dentistry [27] as well as in optics and laser technology [28; 29]. Plasmas are not only very efficient in terms of precision cleaning, but also well-established for surface activation by hydrophilisation or hydrophobisation via the plasma-induced attachment of functional groups or monolayers [30; 31]. As a result, the adhesiveness of glues or lacquers can be improved significantly [32]. This fact turns out to be an advantageous feature for the cementing of glasses since in this context one important aspect is the glass surface energy and its polarity, respectively. Depending on the surface tension and polarity of the used cement, replacing polar groups by non-polar, dispersive ones--and vice versa--allows improving the interlocking mechanisms between the glass surface and the cement [26].