Mr. Joachim Hengst Profile

Joachim Hengst

CTO at optoSiC/MERSEN

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Proceedings Article | 23 July 2008 Paper

Optical materials for astronomy from SCHOTT: the quality of large components

Ralf Jedamzik, Joachim Hengst, Frank Elsmann, Christian Lemke, Thorsten Döhring, Peter Hartmann

Proceedings Volume 7018, 70180O (2008) https://doi.org/10.1117/12.788815

KEYWORDS: Birefringence, Glasses, Silica, Refractive index, Telescopes, Interferometers, Temperature metrology, Wavefronts, Astronomy, Crystals

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The new generation of survey telescopes and future giant observatories such as E-ELT or TMT do not only require very fast or very large mirrors, but also high sophisticated instruments with the need of large optical materials in outstanding quality. The huge variety of modern optical materials from SCHOTT covers almost all areas of specification needs of optical designers. Even if many interesting optical materials are restricted in size and/or quality, there is a variety of optical materials that can be produced in large sizes, with excellent optical homogeneity, and a low level of stress birefringence. Some actual examples are high homogeneous N-BK7 blanks with a diameter of up to 1000 mm, CaF2 blanks as large as 300 mm which are useable for IR applications, Fused Silica (LITHOSIL^®) with dimensions up to 700 mm which are used for visible applications, and other optical glasses like FK5, LLF1 and F2 in large formats. In this presentation the latest inspection results of large optical materials will be presented, showing the advances in production and measurement technology.

Proceedings Article | 1 June 1991 Paper

Influence of the laser-induced temperature rise in photodynamic therapy

Wolfgang Gottschalk, Joachim Hengst, Ronald Sroka, Eberhard Unsoeld

Proceedings Volume 1427, (1991) https://doi.org/10.1117/12.44117

KEYWORDS: Tumors, Skin, Photodynamic therapy, Temperature metrology, Laser therapeutics, Tissue optics, Laser tissue interaction, Magnesium, Animal model studies, Body temperature

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The influence of laser-induced temperature increase in transcutaneous PDT was examined in this study. First the subcutaneous temperature and the relative light intensity between tumor and skin were measured as a function of the applied power density in a series of studies. In a second experiment the influence of temperature on the effect of photodynamic therapy was studied. Determination of temperature and of relative light intensity was performed on three groups of mice: one group of C3H mice with macroscopically strong pigmentation, a second group of the same species with weak pigmentation and a third group of extensively unpigmented, homozygote nude mice of the NMRI family were used. For the second series of experiments the SSK2 fibrosarcoma was used as a tumor model on the C3H mouse. The photosensitized tumors from three animal groups, each with 5 animals, were irradiated subcuratively. In Group 1 the tumor surface was cooled in order to prevent laser- induced temperature effects. In Group 2 and 3 no cooling was used. Evaluation of the therapeutic effect was performed in respect to the regrowth delay time. With the use of transcutaneous PDT it could be shown that the temperature and the relative light intensity between tumor and skin depended essentially on the concentration of pigmentation of the skin above the tumor. Dependent on pigmentation and cooling, temperatures of more than 42 degree(s)C were established with irradiation at power densities starting at about 300 mW/cm². In the second series of experiments a clear prolongation of the regrowth delay time, i.e. a better therapeutic effect, was achieved in uncooled irradiated tumors. Curative therapy was successful only in uncooled irradiated tumors. For this reason the synergistic influence of laser-induced hyperthermia on the therapeutical result of PDT could be shown on the tumor model used.

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