Band 11, Heft 5-6

The polarimetric techniques are used in various biomedical applications for a non-contact and fast diagnosis of tissue that is known as optical biopsy approach. These optical modalities provide relevant information on micro-architecture of biological tissue and its alterations induced by different diseases, thus, helping in staging and precise delineation of the pathology zones. In this review, we summarize the work of different research groups on using polarized light for brain tissue studies. This includes the investigations of polarimetric properties of brain tissue (both scattering and optical anisotropy) for brain connectome reconstruction, the visualization of in-plane brain fiber tracts for brain tumor contrast enhancement during neurosurgery, and the histopathology analysis for disease staging in Alzheimer’s subjects. We discuss also further perspectives for the pre-clinical studies of brain with polarized light.

A method for the evaluation of experimental data from spectroscopic ellipsometry is proposed which combines the global-search optimization algorithm with statistical model selection criteria. The hybrid genetic-gradient search algorithm (HGGA) is applied to find the optical parameters and thickness of a diamond-like carbon (DLC) coating deposited on SW7M stainless steel. Akaike and Bayesian information criteria are used to evaluate the different dielectric function models. The method is able to find optical model parameters even in case of a limited initial knowledge about the material optical constants. At the same time, the optimal dielectric function model for the description of the material optical properties can be selected unambiguously from the set of candidate models.

We performed infrared and time-domain terahertz spectroscopic ellipsometry measurements of thin films of the perovskite antiferromagnetic insulator SrMnO 3 that were grown by pulsed laser deposition (PLD) on LaAlO 3 , SrLaGaO 4 , and LSAT substrates which yield an epitaxial strain ranging from −0.3 to 1.7%. Taking these thin films as a representative example, we discuss the strategies for analyzing the ellipsometry spectra and extracting the information about the thin film dielectric response that can be equally applied to a variety of oxide based thin films and heterostructures. In particular, for the room temperature spectra we show that the three infrared-active phonon modes of the cubic perovskite structure of SrMnO 3 undergo the expected softening with increasing tensile strain. For the SrMnO 3 film on SrLaGaO 4 , we find that the low-energy (TO1) phonon mode reveals anomalous temperature dependence in the vicinity of the Néel temperature of about 170 K that signifies a strong spin-phonon coupling. For the SrMnO 3 film on LSAT, we identify some irreversible changes of the infrared ellipsometry spectra that occur as the sample is heated to elevated temperature up to 560 K. These changes of the ellipsometry spectra have been attributed to a partial oxygen loss of the SrMnO 3 thin film since they can be reverted with a post annealing treatment under high oxygen pressure.

Within the last 10 years the illuminants for automotive exterior lighting shifted nearly completely to LEDs. Due to being semiconductor devices, LEDs behave differently compared to incandescent lamps and xenon bulbs. The paper derives a generalized thermal and geometric LED model. This gains advantage because the data provided in data sheets is different from manufacturer to manufacturer and even from one manufacturer the data is not standardized. So the data is not prepared to be included easily in any development process. In this context “model” mainly refers to a calculation procedure. The data provided in data sheets often has to be digitized. Outgoing from this digitized data a model, based on a smart data combination and polynomial regression, is built up. This model is described in detail and an application to simulations by means of computational fluid dynamics (CFD) is discussed. In doing so a geometric simplification is suggested. This simplification is done in a manner to keep the thermal characteristic of the original LED. The model may be used in different applications such as simulations and design. It allows predicting the thermal status and light output during a virtual development phase, because it inherently calculates the thermal power and light output. This may lead to a more precise estimation of temperatures in lighting systems as well as a prediction of hot lumens.

In the field of precision optics, more and more glass materials that are difficult to machine are being used because of their interesting optical properties. At the same time, the geometries are getting more demanding and the tolerances to be achieved are tighter. The establishment of an efficient process chain is therefore becoming an ever-greater challenge. Particularly in the field of CMP, knowledge of the machining properties of pads and slurries are required to design efficient processes. This knowledge has to be gained through time-consuming in-house tests, as the manufacturers of the consumables are usually only able to provide basic data. In addition, the boundary conditions under which the data were collected are often incomplete defined and thus not comparable. The novel methodical procedure presented here for the initial design of CMP processes is based on a standardized procedure for carrying out the tests. From the resulting database, a starting point for the design of own processes can be identified quickly and unerringly. This article describes the structure of the procedure as well as the necessary background. In addition, the visualization and the procedure for selecting start parameters are discussed using an example application.