Joining processes that do not require joining materials are increasingly needed as an alternative to classic fine cementing in optical production to meet the growing quality requirements. In order to satisfy this demand, processes such as direct bonding (e.g. silicone on insulators) have been adopted successfully from the wafer industry and transferred to fused silica in optical industry after further development [1]. So far, optical contact bonding has only been tested on pure fused silica or coated fused silica [2, 3] where the underlying bonding mechanism is known very well and described in detail [4]. As part of own previous work [5], a process based on a dielectric barrier discharge plasma at atmospheric pressure was developed so that fused silica optics with very sensitive functional optical layers could also be successfully bonded for the first time. In this contribution, the further development of this approach for bonding of Schott’s N-BK7 as one of the most common and used optical glasses is introduced. It differs from fused silica in terms of chemical composition, manufacturing qualities and optical properties. It was successfully bonded with the developed process and mentionable high bond strengths were achieved. Possible bonding mechanisms leading to the different bond strengths are discussed here.
Mechanical abrasion is usually accepted to be the predominant mechanism during material removal of glass via grinding. However, a certain chemical reaction of the used lubricant with the glass surface as occurring during polishing can be expected. Against this background, the impact of different types of water as lubricants, tap water and distilled deionised water, on surface roughness and the degree of contamination of bound abrasive ground heavy flint glass surfaces was investigated in this contribution. It is shown that in case of distilled deionised water, notably lower surface roughness is obtained. Moreover, huge differences in the presence of hydrogen and calcium were qualitatively measured via laserinduced breakdown spectroscopy. The results indicate that the type of water, and especially its content of mineral trace elements, has a mentionable impact on the grinding process and the state of the ground surface. Smoother surfaces with a lower amount of contaminations were achieved when using distilled deionised water in the course of the grinding process. This fact is of mentionable interest for the production of optical components where usually, optically inactive surfaces remain in the ground state.
Liquid-based lenses are of notable interest for the realization of prototypes, small batch series and even mass-product articles as for example micro lens arrays or low-cost optics. Hence, quite a number of different approaches for the manufacture of such lenses are in hand. The focal length of liquid lenses can be customized by the choice of the used liquid, a modification of its viscosity, for example via heating, substrate coating or overhead storing and curing. In this contribution, we present a further approach based on plasma treatment of the substrate surface where two different effects are generated by the use of different process gases. After treatment, optical cement is applied to the surfaces, forming a plano-convex lens due to surface tension. Argon plasma treatment leads to a reduction of the contact angle and an increase in the focal length of the lens in the course of treatment. The opposite effect, an increase in contact angle and a decrease in focal length, respectively, occurs when using octafluorocyclobutane as process gas. The possible range of currently realizable focal lengths and the particularly underlying effects are presented in this contribution.
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.
This Conference Presentation, "Investigation of non-uniformity of classically polished fused silica surfaces via laser-induced breakdown spectroscopy," was recorded at SPIE Optical Metrology 2019 held in Munich, Germany.
We report on a lecture course model that we established three semesters ago in order to strengthen practice-orientated teaching in optics and photonics: In the frame of the lecture “Advanced Laser Treatment”, which is a mandatory course of our university’s master degree curriculum, students now have the possibility to experience a researcher’s every-day tasks. In small groups, the attendees work on a self-contained topic which is defined by the lecturers. The work load and content is in the scale of a small work package of a usual research project. It includes the initial research on the state of the art, the experimentation using different laser sources, and the subsequent evaluation of the obtained results. On the basis of this work, the students then prepare a draft of a scientific paper and finally present their results and findings orally in a conference-like exam. This lecture course model has turned out to be an appropriate teaching method for practice-orientated subjects. It was observed that the students are much more motivated and work more independently than during a classical lecture with a certain amount of lab work. Having sole responsibility supports to identify with their project. Further, this lecture course model helps to develop scientific work skills, attain first experience in every-day research tasks and encourages creativity. In some cases, the paper drafts written by the students can even be published, representing a valuable starting point for their future professional career.
Geometric optics is at the heart of optics teaching. Some of us may remember using pins and string to test the simple lens equation at school. Matters get more complex at undergraduate/postgraduate levels as we are introduced to paraxial rays, real rays, wavefronts, aberration theory and much more. Software is essential for the later stages, and the right software can profitably be used even at school. We present two free PC programs, which have been widely used in optics teaching, and have been further developed in close cooperation with lecturers/professors in order to address the current content of the curricula for optics, photonics and lasers in higher education. PreDesigner is a single thin lens modeller. It illustrates the simple lens law with construction rays and then allows the user to include field size and aperture. Sliders can be used to adjust key values with instant graphical feedback. This tool thus represents a helpful teaching medium for the visualization of basic interrelations in optics. WinLens3DBasic can model multiple thin or thick lenses with real glasses. It shows the system focii, principal planes, nodal points, gives paraxial ray trace values, details the Seidel aberrations, offers real ray tracing and many forms of analysis. It is simple to reverse lenses and model tilts and decenters. This tool therefore provides a good base for learning lens design fundamentals. Much work has been put into offering these features in ways that are easy to use, and offer opportunities to enhance the student’s background understanding.
In this contribution, we report on a laser-chemical removal method for precise machining of micro forming tools.
Thereby, a focused machining laser beam is guided coaxially to an etchant jet stream. Since the material removal is
caused by laser-induced chemical reactions using this method, machining is achieved at low laser powers. Hence,
material stressing involving micro cracks and further parasitic effects can be avoided. Due to these advantages, this
method offers a suitable technique for the finishing of precision micro tools. Several experiments have been performed at
rotary swaging jaws made of Stellite 21 in order to chamfer the edged transition section between the operating sphere
and the tool flank. The influence of both different laser powers and work piece traverse speeds has been investigated. For
this purpose, several parallel laser paths were applied along the edged transition section when varying the process
parameters. Here, the incident laser beam is subjected to different angles of incidence. Due to reflection effects, the
process parameters have to be matched with respect to the particular angle of incidence during the machining. In this
vein, the edged transition section of rotary swaging jaws was chamfered at radii in the range of 120 μm.
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