Lang, Walter
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Preferred name
Lang, Walter
Official Name
Lang, Walter
Alternative Name
Lang, W.
ORCID
GND
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Item-typ:Veröffentlichung, Design and evaluation of a freeform lens-array for a structured light illumination(Optica Publishing Group, 2021); ; ; ; In illumination applications, freeform lens design starts by modeling the light source intensity, then determining the lens surface. Therefore, any change in the source intensity distribution directly impacts the created illuminance. Freeform lens-array could reduce the dependency between the illuminance pattern and the source intensity distribution. It divides the light source energy into separate beams; each creates the same illuminance pattern. All separated beams are superimposed at a distant target to generate the final illuminance pattern. This paper explains the design procedures of a freeform lens-array in detail, simulates the optical performance, and experimentally evaluates the working principle. Experiments evaluate using different light sources and using a variable illuminated aperture. Moreover, simulations compare the freeform lens-array to a traditional freeform lens.Wissenschaftlicher ArtikelBand:4Heft:390 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Characterization of specular freeform surfaces from reflected ray directions using experimental ray tracing(Simplified Spelling Society, 2021-10); ; ; ; The applications of freeform surfaces in optical components and systems are increasing more and more. Therefore, appropriate measurement techniques are needed to measure these freeform surfaces for verification. This task is still a challenge for most measurement techniques. In this paper, we propose a measurement technique for optical and other specular freeform surfaces based on experimental ray tracing. This technique is able to measure form and mid-spatial-frequency deviations simultaneously. The focus will be set on the sensing technique and the measurement uncertainties in the setup. As the measurement technique is described, an estimation of the influence of different uncertainties based on simulations is given. The result from an experimental measurement is evaluated in relation to the influence of the uncertainties. A comparison measurement for evaluation is given.Wissenschaftlicher ArtikelBand:10Heft:279 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, On thermal stability and decomposition mechanisms of aromatic diamines employed as links in novel Pt nanoparticle network catalysts(Elsevier, 2023-01-05); ; ; The thermal stability of microporous networks of Pt nanoparticles interlinked by p-Phenylenediamine (PDA) was investigated by temperature-programmed desorption spectroscopy (TPD) and transmission electron microscopy (TEM). The detection of aniline, benzene, and NH3 as major desorbing fragments in TPD revealed cleavage of the C-N bonds in PDA as a major route of thermally induced decomposition, probably via hydrogenolysis assisted by dehydrogenation reactions of PDA running alongside. Varying the Pt:PDA ratio in the networks demonstrated that the Pt nanoparticles catalytically promote the decomposition of their PDA links. A quantitative analysis of the TPD spectra indicated that the thermal stability of PDA strongly correlates with the number of bonds (0, 1 or 2) formed by the amino groups of an individual PDA molecule with Pt. Only the most stable PDA species appears to be of relevance for the structural stability of the nanoparticle network, as heating experiments with in situ TEM showed. The results have strong implications for the application of PDA-linked Pt nanoparticles as heterogeneous catalysts in hydrogen gas microsensors where the choice of operating temperature has to balance maximization of signal-to-noise ratio and maintenance of structural stability. An anealing step up to 450–500 K after synthesis of the catalyst is suggested in order to optimize its catalytic activity by removing PDA species that are not essential for structural stabilty.Wissenschaftlicher ArtikelBand:656, Part A57 50 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Characterization of a highly sensitive and selective hydrogen gas sensor employing Pt nanoparticle network catalysts based on different bifunctional ligands(Elsevier, 2020-11-01); ; ; ; A catalytic hydrogen gas sensor of superior sensitivity, selectivity, resolution and dynamic response was developed with catalysts composed of ligand-stabilized Pt nanoparticles. We have characterized different catalysts utilizing the bi-functional ligands trans-1,4-diaminocyclohexane (DACH), 1,5-diaminonaphthalene (DAN), 4,4´´-diamino-p-terphenyl (DATER), benzidine (BEN) and p-phenylene diamine (PDA) for hydrogen gas sensing. A comprehensive evaluation by comparison, with respect to both, structural aspects (TEM and SEM) and gas sensing performance of the 5 types of ligand-linked Pt nanoparticles and non-stabilized Pt nanoparticles was conducted to select the optimized catalysts. From this investigation, DATER-linked Pt nanoparticles appear immensely promising: the sensor is selective to hydrogen and shows extremely high sensitivity, around 400 mV/1% vol., but exhibits no crosssensitivity to methane and ethane. Likewise, sensors with DATER- and DAN-linked Pt nanoparticles can detect down to 0.001 % (10 ppm) alongside 650 ms average response time (t90).Wissenschaftlicher ArtikelBand:32245 40