Dr. Rainer Jaschek Profile

Dr. Rainer Jaschek

at Schott AG

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Publications (2)

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Proceedings Article | 2 May 2005 Paper

Development of a new process for manufacturing precision gobs out of new developed low Tg optical glasses for precise pressing of aspherical lenses

Rainer Jaschek, Christopher Klein, Christian Schenk, Klaus Schneider, Jochen Freund, Simone Ritter

Proceedings Volume 10315, 103150G (2005) https://doi.org/10.1117/12.605693

KEYWORDS: Glasses, Polishing, Aspheric lenses, Optics manufacturing, Optical components, Lenses, Chemical elements, Lens grinding, Precision glass molding, Neodymium

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Aspherical lenses or refractive elements out of optical glass can be produced either by grinding and polishing of glass or by precise molding of glass preforms. The first process is applied for lenses with larger geometries and smaller production quantities. On the other hand, precise molding is used for volume production of lenses within a diameter range between 1 mm and around 30 mm. The addressed products can be found in the consumer markets (digital imaging, digital projection and digital storage). Different preform types can be used for precise molding: polished spherical near shape preforms, polished balls, polished discs and precision gobs. The latter are made directly from the glass melt. This paper describes a newly developed process, which results in fire-polished gobs with very low surface roughness and excellent volume accuracy. Since precision gobs are mostly made for precise molding, they must meet specific process requirements apart form their optical values, such as allowing low molding temperatures and shorter process cycles times. Therefore, this paper also describes the latest results in the development of low Tg glasses, which are designed for the volume production of precision molded optical components. Beside the important parameters like nd, nd as well as Tg, other properties like chemical durability, devitrification resistance, thermal expansion and conductivity coefficients are important for optimizing the precise molding process. The characteristics of three new low Tg glasses in the FK-, PK- as well as SK-region are presented. These glasses are environmentally friendly, since they are free of lead and arsenic.

Proceedings Article | 31 March 1995 Paper

Contribution to the beam plasma material interactions during material processing with TEA CO2 laser radiation

Rainer Jaschek, Peter Konrad, Roland Mayerhofer, Hans Bergmann, Peter Bickel, Roland Kowalewicz, Alfred Kuttenberger, Jens Christiansen

Proceedings Volume 2502, (1995) https://doi.org/10.1117/12.204893

KEYWORDS: Plasma, Titanium, Atmospheric plasma, Pulsed laser operation, Materials processing, Aluminum, Photography, Atmospheric optics, Spectroscopy, Diagnostics

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The TEA-CO₂-laser (transversely excited atmospheric pressure) is a tool for the pulsed processing of materials with peak power densities up to 10¹⁰ W/cm² and a FWHM of 70 ns. The interaction between the laser beam, the surface of the work piece and the surrounding atmosphere as well as gas pressure and the formation of an induced plasma influences the response of the target. It was found that depending on the power density and the atmosphere the response can take two forms. (1) No target modification due to optical break through of the atmosphere and therefore shielding of the target (air pressure above 10 mbar, depending on the material). (2) Processing of materials (air pressure below 10 mbar, depending on the material) with melting of metallic surfaces (power density above 0.5 10⁹ W/cm²), hole formation (power density of 5 10⁹ W/cm²) and shock hardening (power density of 3.5 10¹⁰ W/cm²). All those phenomena are usually linked with the occurrence of laser supported combustion waves and laser supported detonation waves, respectively for which the mechanism is still not completely understood. The present paper shows how short time photography and spatial and temporal resolved spectroscopy can be used to better understand the various processes that occur during laser beam interaction. The spectra of titanium and aluminum are observed and correlated with the modification of the target. If the power density is high enough and the gas pressure above a material and gas composition specific threshold, the plasma radiation shows only spectral lines of the background atmosphere. If the gas pressure is below this threshold, a modification of the target surface (melting, evaporation and solid state transformation) with TEA-CO₂- laser pulses is possible and the material specific spectra is observed. In some cases spatial and temporal resolved spectroscopy of a plasma allows the calculation of electron temperatures by comparison of two spectral lines.

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