Diploma in Physics at University of Mainz on optical pumping of short-lived Rb-isotopes
Doctorate in physics at Max-Planck-Institute Mainz on Development of Scintillation Glasses
Quality assurance and application of optical glasses, radiation shielding glasses and Zerodur
Projects involved: KECK, CHANDRA, ESO-VLT, i-line glass for Microlithography, HET, GRANTECAN, 4 m mirror blanks, LISA Pathfinder, ESO-ELT
For more than 25 years experience in optical glass, Zerodur and special optical glasses - specification, properties, measurement methods, application consulting, standardization, instruction
Recent specializations
Strength optical glass and zero expansion glass ceramic (ZERODUR),
Development of measurement methods for optical glass,
Dispersion properties of optical glasses,
Lobby work for optical glass and filter glass related to EU directive RoHS
(Awarded with Honorary Bear of German Industrial Federation SPECTARIS 2010 and 2018)
Schott user workshops for optical materials
ISO standardization for optical glass and optical elements
OPTENCE - Photonics competence cluster Hesse / Rhineland-Palatinate, Germany - Member of the Board until 4/2018, Honorary member
DIN German Inst. for Standardization Optics and Precision Mechanics Standards Committee - Vice President until 4/2017
DIN German Inst. for Standardization Working Group "Optical Materials" - Convener until 1/2018
ISO International Standarization Organization - Working Group "Raw Optical Glass" - Convener until 1/2018
Max-Planck-Institute for Astronomy Heidelberg Germany Member of the Board of Trustees
Doctorate in physics at Max-Planck-Institute Mainz on Development of Scintillation Glasses
Quality assurance and application of optical glasses, radiation shielding glasses and Zerodur
Projects involved: KECK, CHANDRA, ESO-VLT, i-line glass for Microlithography, HET, GRANTECAN, 4 m mirror blanks, LISA Pathfinder, ESO-ELT
For more than 25 years experience in optical glass, Zerodur and special optical glasses - specification, properties, measurement methods, application consulting, standardization, instruction
Recent specializations
Strength optical glass and zero expansion glass ceramic (ZERODUR),
Development of measurement methods for optical glass,
Dispersion properties of optical glasses,
Lobby work for optical glass and filter glass related to EU directive RoHS
(Awarded with Honorary Bear of German Industrial Federation SPECTARIS 2010 and 2018)
Schott user workshops for optical materials
ISO standardization for optical glass and optical elements
OPTENCE - Photonics competence cluster Hesse / Rhineland-Palatinate, Germany - Member of the Board until 4/2018, Honorary member
DIN German Inst. for Standardization Optics and Precision Mechanics Standards Committee - Vice President until 4/2017
DIN German Inst. for Standardization Working Group "Optical Materials" - Convener until 1/2018
ISO International Standarization Organization - Working Group "Raw Optical Glass" - Convener until 1/2018
Max-Planck-Institute for Astronomy Heidelberg Germany Member of the Board of Trustees
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The Weibull distribution is the model used traditionally for the representation of such data sets. It is based on the weakest link ansatz. The use of the two or three parameter Weibull distribution for data representation and reliability prediction depends on the underlying crack generation mechanisms. Before choosing the model for a specific evaluation, some checks should be done. Is there only one mechanism present or is it to be expected that an additional mechanism might contribute deviating results? For ground surfaces the main mechanism is the diamond grains’ action on the surface. However, grains breaking from their bonding might be moved by the tool across the surface introducing a slightly deeper crack. It is not to be expected that these scratches follow the same statistical distribution as the grinding process. Hence, their description with the same distribution parameters is not adequate. Before including them a dedicated discussion should be performed.
If there is additional information available influencing the selection of the model, for example the existence of a maximum crack depth, this should be taken into account also. Micro cracks introduced by small diamond grains on tools working with limited forces cannot be arbitrarily deep. For data obtained with such surfaces the existence of a threshold breakage stress should be part of the hypothesis. This leads to the use of the three parameter Weibull distribution. A differentiation based on the data set alone without preexisting information is possible but requires a large data set. With only 20 specimens per sample such differentiation is not possible. This requires 100 specimens per set, the more the better.
The validity of the statistical evaluation methods is discussed with several examples. These considerations are of special importance because of their consequences on the prognosis methods and results. Especially the use of the two parameter Weibull distribution for high strength surfaces has led to non-realistic results. Extrapolation down to low acceptable probability of failure covers a wide range without data points existing and is mainly influenced by the slope determined by the high strength specimens. In the past this misconception has prevented the use of brittle materials for stress loads, which they could have endured easily.
Optical glass provides a central function in optical systems: the precisely defined refraction of light with the highest throughput. Large parts of the optical industry depend on this key material. Microscopes, binoculars, cameras, and projectors constitute examples that are unthinkable without optical glass. Their properties, however, differ considerably from those of other technical materials such as metals or plastics. Datasheet values of refractive index extend to five decimal places (e.g. 1.51680) and homogeneity might be specified to even two more digits (e.g. 2x10-7). This extreme precision sets optical glass apart from most other materials. For optical glass users it is important to know facts about its production and properties in order to specify optical elements adequately. Engineering drawing requirements must ensure sound function of the optical system but should do so without over-specifying various attributes which might lead to higher costs, delivery time delay, or even non-availability. Application formats extend from the millimeter range up to about one meter. For small parts, glass properties are usually not expected to be critical. Most properties, however, do not scale up linearly with the sample size. For large lenses and prisms, different scaling laws of glass properties must be taken into consideration in order to obtain suitable quality. For designing and purchasing of optical elements it is very useful to know the technical conditions of producing, post-processing, quality inspection, and application of optical glass. This course provides knowledge about glass types and properties, including definitions, tolerances, and measurement methods. Relevant properties to be discussed include refractive index, dispersion, transmission, homogeneity, striae, stress birefringence. Also covered are production processes and their influences on glass properties, raw glass delivery formats. The course covers specification of lenses and prisms for optical systems according to the international standards ISO 10110 (optical elements) and ISO 12123 (raw optical glass). Finally, availability of optical glasses and restrictions thereof due to technical, economic, and regulatory reasons are covered.
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