Cemented optical components and groups are essential devices for the realisation of modern systems and apparatuses used in a broad range of different applications such as telecommunications, imaging and even surgery. However, various parameters may affect the stability of cemented connections. In this context, the impact of dielectric barrier discharge plasma at atmospheric pressure on the adhesiveness of cemented glass components was evaluated in the present work. For this purpose, the plasma-induced change in surface wettability and energy as well as the cement's adhesive pull strength was measured. Investigations were performed on samples, which were subject to different procedures of artificial ageing. It is shown that the adhesive pull strength of cemented glass components was notably increased after a short-term plasma treatment of merely 10 s due to an enhanced wettability of the applied UV-curing optical cement. The pull strength, i.e., the adhesiveness of cemented glasses was increased by a factor of 2.1 to 4.6, depending on the particularly applied artificial ageing procedure. The results and findings finally demonstrate the high potential of the applied short-term plasma treatment as a cleaning and surface activation step in optics manufacturing on an industrial scale.

In this contribution, we report on the impact of direct dielectric barrier discharge argon plasma at atmospheric pressure on femtosecond laser engraving of aluminium. It is shown that the assisting plasma strongly affects the surface geometry and formation of spikes of both laser-engraved single lines and patterns of adjacent lines with an appropriate overlap. Further, it was observed that the overall ablation depth is significantly increased in case of large-scale patterning whereas no notable differences in ablation depth are found for single lines. Several possible mechanisms and underlying effects of this behaviour are suggested. The increase in ablation depth is supposed to be due to a plasma-induced removal of debris particles from the cutting point via charging and oxidation as supported by EDX analysis of the re-solidified debris. Furthermore, the impact of a higher degree of surface wrinkling as well as direct interactions of plasma species with the aluminium surface on the ablation process are discussed.

The combination of laser and low-temperature plasmas is of growing interest for micro-structuring purposes for a wide range of materials. This combination can be used for a reduction of the ablation threshold as well as an improvement of the machining quality in various laser material processing applications. The plasma involved in such combination, however, leads to a thermally generated influence on the laser beam quality. In this paper, a DBD-based argon plasma as typically used in low-temperature laser plasma hybrid arrangements was investigated by interferometric and beam profile measurements. The radial temperature profile as well as the beam propagation characteristics in terms of focal shift and effective pointing stability was determined. Due to the argon plasma, a temperature increase ΔT by up to 25 K, and thus a thermal lens was observed within the light path of the laser beam featuring an increase in refractive index Δn by maximum 2.86 × 10−5. In the given setup, the plasma-induced thermal lens caused a focal shift by up to 4 mm. Further, the lateral focus position was deviated by a maximum of about 30 µm, which is in the order of magnitude of the beam waist radius.

We report on an atmospheric pressure plasma (APP) treatment of fused silica and its related surface and near-surface effects. Such treatment was performed in order to improve laser micro-structuring of fused silica by a plasma-induced modification of the glass boundary layer. In this context, an APP jet applying a hydrogenous process gas was used. By the plasma treatment, the transmission of the investigated glass samples was significantly decreased. Further, a decrease in the superficial index of refraction of approx. 3.66 % at a wavelength of 636.7 nm was detected ellipsometrically. By surface energy measurements, a decrease of the surface polarity of 30.23 % was identified. These determined modifications confirm a reduction of silicon dioxide to UV-absorbing silicon suboxide as already reported in previous work. Further, a change in reflexion by maximum 0.26 % was detected which is explained by the superposition of constructive and destructive interferences due to a surface wrinkling. With the aid of atomic force microscopy, an increase of the surface root mean squared roughness by a factor of approx. 19 was determined. It was found that both the surface energy and the strength of the fused silica surface were reduced by the plasma treatment. Even though such treatment led to a clustering of carbonaceous contaminants, a surface-cleaning effect was confirmed by secondary ion mass spectroscopy and energy-dispersive X-ray spectroscopy. The increase in UV-absorption allows enhanced laser ablation results as shown in previous work.

In this work, a common-path interferometer including integrated single-prism beam shaping is presented. Both theoretical considerations and experimental results on single-prism shaping of elliptical and circular laser beams were performed. Based on a single-prism beam shaper, a common-path interferometer without any classical beam splitter device was assembled and characterised. It is shown that the presented setup provides well-evaluable interference patterns with a Michelson contrast of 0.42-0.45. (c) 2012 Elsevier Ltd. All rights reserved.

In this contribution, we report on a novel hybrid laser-plasma method for material processing applications. This method is based on the combination of both an ArF excimer laser (λ = 193 nm) and a low-temperature atmospheric pressure plasma jet source for the chemical reduction of glass surfaces. Here, a hydrogen-containing plasma gas was applied. Due to the layer of silicon suboxide that is generated in this vein, the absorption of the incoming machining laser beam is significantly increased after 15 minutes of plasma-treatment. Several machining experiments in terms of frontside ablation were performed on fused silica. Here, both pure and plasma-treated surfaces were ablated using single laser pulses with a pulse duration of 20 ns. By introducing the presented hybrid technique, the ablation threshold for micro-structuring was reduced significantly by a factor of 4.6 whereas the peak-to-valley height Rz of the machined area was decreased by a factor of 2.3. Further, back-side ablation using the presented method was considered. By a terminal tempering process, the initial transmission characteristics of fused silica can be reconstituted.

A low-temperature atmospheric pressure plasma jet was used for chemical reduction of fused silica. For this purpose, a hydrogen-containing plasma was applied. A silicon suboxide layer was generated and hydrogen was implanted into the bulk material. Changes in stoichiometry, concentration of hydrogen and optical transmission were determined. An ArF excimer laser was used for the ablation of untreated and plasma-treated fused silica. The ablation threshold was significantly decreased by a factor of 4.6 in case of plasma treated substrates. Furthermore, in multi-pulse experiments, the ablation rate remained constant at least up to a depth of 10.5μm.

We report on atmospheric pressure argon plasma-based surface treatment and hybrid laser-plasma ablation of barite crown glass N-BaK4 and heavy flint glass SF5. By pure plasma treatment, a significant surface smoothing, as well as an increase in both the surface energy and the strength of the investigated glass surfaces, was achieved. It was shown that for both glasses, hybrid laser plasma ablation allows an increase in the ablation depth by a factor of 2.1 with respect to pure laser ablation. The ablated volume was increased by an averaged factor of 1.5 for N-BaK4 and 3.7 for SF5.

In this Letter, we report on the near-surface modification of fused silica by applying a hydrogenous atmospheric pressure plasma jet at ambient temperature. A significant decrease in UV-transmission due to this plasma treatment was observed. By the use of secondary ion mass spectroscopy, the composition of the plasma-modified glass surface was investigated. It was found that the plasma treatment led to a reduction of a 100 nm thick SiO2 layer to SiOx of gradual depth-dependent composition. For this plasma-induced layer, depth-resolved characteristic optical parameters, such as index of refraction and dispersion, were determined. Further, a significant plasma-induced increase of the concentration of hydrogen in the bulk material was measured. The decrease in transmission is explained by the plasma-induced near-surface formation of SiOx on the one hand and the diffusion of hydrogen into the bulk material on the other hand.

In this paper, we present a hybrid laser-plasma ablation method for material processing applications. For this purpose, a coaxial configuration consisting of a low-temperature atmospheric pressure argon plasma beam and a Nd:YAG-laser at a wavelength of 355 nm was used. Both pure laser ablation and hybrid laser-plasma ablation experiments were performed on aluminum at different laser energies and numbers of laser pulses. In the case of hybrid ablation, both the depth and volume ablation rates were increased significantly in comparison to pure laser ablation. This effect is described by a linear interrelationship of both the ablation rate and the particularly applied laser energy and is thus due to energetic synergies. Such behavior can be explained by the de-excitation of argon plasma species and an accompanying energy deposition at the generated debris and the sample surface. The energetic effect was found to abate with increasing ablation depth. However, considerable improvements in terms of ablation rate are achieved in the near-surface depth range of approx. 500 microns.

Kurzfassung Im Rahmen des Niedersächsischen Innovationsverbunds Plasmatechnik (NIP) werden neue Anwendungen der Plasmatechnologie in den Bereichen Fertigungstechnik und Materialanalyse bis hin zur Medizintechnik erschlossen sowie ihr ökonomischer und ökologischer Nutzen evaluiert. Im Bereich der Materialanalyse zählt dazu die Entwicklung eines spektroskopischen Verfahrens unter Nutzung eines ökoeffizienten Atmosphärendruckplasmas zur Emissionsanregung. Zum Einsatz kommt hierbei eine im Rahmen des Projekts entwickelte neuartige Plasmaquelle, die für die Analyse gasförmiger, flüssiger und fester Proben in unterschiedlichen Modi betrieben werden kann. Der Energieeintrag in das Probenmaterial durch diese Plasmaquelle beträgt hierbei wenige Mikrojoule. An verschiedenen Probenmaterialien wurde gezeigt, dass sich dieses Verfahren zur Erzeugung und Detektion elementspezifischer Spektrallinien eignet.

Plasma-Based Ionisation Spectroscopy for Material Analysis. In the frame of the Lower Saxony Innovation Network for Plasma Technology (NIP), new applications of plasma technologies in manufacturing and medical technology, analysis and diagnostics as well as its industrial advantages are evaluated. This work includes the development of a spectroscopic method, based on ecological efficient atmospheric pressure plasma for excitation of emission. Here, a novel plasma source is used. This plasma source was developed in the frame of the project and can be run in different modes of operation. The resulting application of energy amounts to some microjoule. By investigations of different sample materials, the suitability of this method for detecting characteristic spectral lines was shown.

A low-current and low-compression z-pinch nitrogen plasma is heated up by means of a short laser pulse. Spectra are taken in the extreme ultraviolet spectral range from 11 to 18 nm to estimate the heating effect. Without additional laser heating the initial plasma conditions are ne≈1017 cm−3 and Te≈11 eV. The additional laser heating causes an increase in the electron temperature of about a factor of 5 to Te≈57 eV, whereas the electron density nearly remains at the initial value. The experimentally determined values are compared to the results obtained by means of simulations and are in fairly good agreement.

Extreme ultraviolet (EUV) spectroscopy has been carried out on a xenon plasma generated using a hollow-cathode-triggered Z-pinch discharge. The temporal behavior of the electron temperature was estimated from the analysis of spectral data. The electron temperature measurements have been performed by the Boltzmann plot method using Xe I and Xe II lines. Furthermore, an analytical collisional-radiative model was used to calculate the EUV spectra in the wavelength range from 13 to 16 nm for different electron temperatures. The measured relative line intensities from EUV spectra of Xe 9+ and Xe 10+ ions were compared to the results of the calculation. Fairly good agreement has been found between the experiments and the model calculations. These results indicate that a high effective charge number can be achieved by a low current and low-pressure pinch.