Edgar Pawlowski

Reference based optical characterization of glass-ceramic converter for high power white LEDs

Fluorescence techniques are known for their high sensitivity and are widely used as analytical tools and detection methods for product and process control, material sciences, environmental and bio-technical analysis, molecular genetics, cell biology, medical diagnostics and drug screening. According to DIN/ISO 17025 certified standards are used for fluorescence diagnostics having the drawback of giving relative values for fluorescence intensities only. Therefore reference materials for a quantitative characterization have to be related directly to the materials under investigation. In order to evaluate these figures it is necessary to calculate absolute numbers like absorption/excitation cross section and quantum yield. This can be done for different types of dopants in different materials like glass, glass ceramics, crystals or nano crystalline material embedded in polymer matrices. Here we consider a special type of glass ceramic with Ce doped YAG as the main crystalline phase. This material has been developed for the generation of white light realized by a blue 460 nm semiconductor transition using a yellow phosphor or converter material respectively. Our glass ceramic is a pure solid state solution for a yellow phosphor. For the production of such a kind of material a well controlled thermal treatment is employed to transfer the original glass into a glass ceramic with a specific crystalline phase. In our material Ce doped YAG crystallites of a size of several µm are embedded in a matrix of a residual glass. We present chemical, structural and spectroscopic properties of our material. Based on this we will discuss design options for white LEDs with respect to heat management, scattering regime, reflection losses, chemical durability and stability against blue and UV radiation, which evolve from our recently developed material. In this paper we present first results on our approaches to evaluate quantum yield and light output. Used diagnostics are fluorescence (steady state, decay time) and absorption (remission, absorption) spectroscopy working in different temperature regimes (10 - 350 K) of the measured samples in order to get a microscopic view of the relevant physical processes and to prove the correctness of the obtained data.

New heavy metal oxide silicate amplifier glass for compact and broadband amplifiers

Properties of a new rare-earth doped heavy metal oxide containing silicate glass are presented. The glass has potential for fabrication of ultra-short wideband fiber and planar waveguide amplifiers. We report specific results for a fiber amplifier geometry, discussing achieved improvements in device compactness (Giles gain g* = 210 dB/m allowing up to 100 times shorter fiber) and amplification bandwidth (50% more bandwidth in C-/L-band) compared to the conventional EDFA. We also access the potential of this material for fabrication of active planar integrated waveguide devices.

CPV semi-dense array design for dish and tower collectors

SST is developing a new Dish CPV dense array system that overcomes the flux uniformity requirement of previous designs. The ability to operate without flux uniformity relaxes the precision requirements of primary collector optics and eliminates homogenizing optics previously required for dense array CPV. Array design can be configured for dish and tower/heliostat systems developed for thermal CSP applications. The design uses industry standard CPV cells and manufacturing materials and methods for minimum cost and high reliability. Nominal input flux to the array for full power is about 250 suns. Internal array optics increase flux to the cells to about 1200 suns. Linear optics provide additional concentration, permit novel use of commercial glass production methods and facilitate power collection design that is integrated with dynamic power conversion and maximum power point tracking (MPPT). Efficient power hybrid packaging methods are used along with advanced liquid cooling “cold-plate” thermal management. Byproduct “waste heat” can be provided for on-site CHP use. We report on the design approach and status of development with the beginning of on-sun alpha testing of the first of 50 kW of CPV modules being produced.

Diffractive optical elements fabricated by precise pressing of glass

This paper discusses the precise pressing technology for the fabrication of diffractive optical elements (DOEs). The new established fabrication process allows mass production of DOEs in high homogeneous optical glasses. Our precise pressing process guarantees a very constant quality over the complete production chain. Glass DOEs made by SCHOTT AG are planar optical phase elements with highly accurate shape and efficiency. The blazed profile of the diffractive optical elements was approximated by a stepped profile with up to sixteen phase levels. The highest measured diffraction efficiency for sixteen level gratings was 95%.

Yb:YAG composite ceramic laser

Yb:YAG ceramic laser materials, fabricated by vacuum sintering technology, were optically investigated within different laser set-up configurations. The established nanopowder vacuum sintering process shows good potential for mass fabrication of multicomposite ceramic laser materials with different dopant concentrations. 5%, 7%, 10% single dopant and 7%/20% core-cladding multi-composite Yb:YAG materials were fabricated and investigated. The highest measured slope efficiency, for the composite ceramic laser materials was 81%, at 1030 nm emission wavelength, similar to Yb:YAG single crystals.

Diffractive optical elements fabricated for beam shaping of high-power diode lasers

This paper discusses the use of diffractive optical elements (DOEs) and micro-optics fabricated by precise pressing in glass for beam shaping of high-power diode lasers. The DOEs are used to diffract the light into the point of interest and to improve the laser beam quality. We have realized circular, flat-top and multi-beam intensity profiles. The highest measured diffraction efficiency was higher than 95 %. The new established fabrication process has potential for mass production of DOEs. SCHOTTs precision glass molding process guarantees a very constant quality over the complete production chain.