Beam characterization by phase retrieval solving the transport-of-intensity-equation.

A new method for the characterization of coherent laser beams is proposed. It is based on the non-iterative solution of the transport-of-intensity-equation. The phase to recover is decomposed into paraxial properties of laser beams and a set of lateral shifted radial basis functions, which allows for the derivation of a direct solution of the phase by a least-squares fit without the need of an initial guess. The method is tested with synthetic data to deduce an accuracy metric. Additionally, two real laser beams are characterized. Including the real light source in terms of the reconstructed field allows for a more holistic simulation of optical systems.

Fast computation and characterization of perturbed Bessel-Gauss beams.

In this paper, an extended definition of the Strehl ratio is introduced for Bessel-Gauss (BGB) beams, which, in contrast to classical beams, are not defined at a single point but along the optical axis. For that purpose, the Fresnel diffraction integral is solved analytically to calculate the on-axis field of a BGB that is perturbed by spherical aberration, astigmatism, and coma. Certain approximations are introduced, discussed, and tested against a rigorous propagation method. The derived expression is applied to tolerancing of an example system.

[Measuring, assessing, acting: A practice test of quality indicators for coronary heart disease]. / Messen, Bewerten, Handeln: Qualitätsindikatoren zur Koronaren Herzkrankheit im Praxistest.

BACKGROUND: There are only limited possibilities for doctors in outpatient services to establish quality management that is based on data-driven feedback regarding the quality of health care. However, transparency about one's own activities is a prerequisite for refining this quality. The aim of this project was to make the quality of care for patients with coronary heart disease (CHD) more transparent, use this as a basis to initiate improvement processes, and explore the framework conditions and factors promoting or inhibiting the intended improvement of health care quality. METHOD: 48 general practitioners (GPs) in 32 GP practices from a Bavarian doctors' network (Qualität und Effizienz, QuE) participated in the project. On the basis of claims data from the AOK-Bayern (a statutory health insurance in Bavaria), data from disease management programs (DMP) and medically documented data, 11 quality indicators for patients with CHD were calculated. The indicator scores were individually presented in feedback reports for each doctor's practice. These were the basis for two quality circles. The indicators were measured again after 12 months, and changes against the baseline measurement were registered. GPs from Bavaria formed the control group. Focus groups with the quality circle moderators and two participant surveys were used to identify promoting and inhibiting factors. RESULTS: The baseline values showed a good level of care. Potential for improvement became apparent for pharmacotherapy with beta blockers and statins. After conducting the quality circles four of the eleven indicators showed an increase as intended ("beta blockers for CHD and cardiac insufficiency", "beta blockers after myocardial infarction", "statins", "successful blood pressure control"). For three of these indicators the increase rates were higher than those in the Bavarian control group. One indicator ("statins") was striking because of the wide variation of practice values suggesting differences in care within the network. The majority of participating doctors regarded the database as valid. Quality circles were highly appreciated as an opportunity for professional exchange among colleagues. The data-based feedback reports helped to make deficits in health care transparent and to identify actions that need to be taken. Barriers to implementing quality improvement measures in clinical practice became apparent. DISCUSSION: Reflecting quality indicators in quality circles can effectively trigger quality improvement processes. Barriers would appear to exist, in particular, to the implementation of measures into daily practice routine. Additional organizational support offered by higher-level quality management structures, IT solutions for patient-related data processing as well as a system of financial compensation, which rewards professional concern for quality, may help to overcome the existing barriers.

Coherent field propagation between tilted planes.

Propagating electromagnetic light fields between nonparallel planes is of special importance, e.g., within the design of novel computer-generated holograms or the simulation of optical systems. In contrast to the extensively discussed evaluation between parallel planes, the diffraction-based propagation of light onto a tilted plane is more burdensome, since discrete fast Fourier transforms cannot be applied directly. In this work, we propose a quasi-fast algorithm (O(N3 log N)) that deals with this problem. Based on a proper decomposition into three rotations, the vectorial field distribution is calculated on a tilted plane using the spectrum of plane waves. The algorithm works on equidistant grids, so neither nonuniform Fourier transforms nor an explicit complex interpolation is necessary. The proposed algorithm is discussed in detail and applied to several examples of practical interest.

Description and reimplementation of real freeform surfaces.

Freeform surfaces are becoming an increasingly exciting opportunity in optical design, in particular when correcting systems with off-axis geometries. Nevertheless, especially when coming to commercial use, the challenges for manufacturing are difficult to handle. The optical quality of a system is perturbed by typical deformations, such as localized figure errors and regular mid-spatial-frequency ripples, that come from the diamond-turning process. In this proposal, we investigated a workflow for analyzing the impact of real optical surfaces on the optical performance for even complex systems. Based on a simple and robust description, the surface is implemented back into the design. While the more localized deviations are analytically described by radial basis functions, the residual ripple structures are covered by a new approach based on the power spectral density. The reimport of optical surfaces back into the design software allows simple estimations for the requirements on manufacturing and the analysis of the realistic impact on system performance.

Optical Activation of Germanium Plasmonic Antennas in the Mid-Infrared.

Impulsive interband excitation with femtosecond near-infrared pulses establishes a plasma response in intrinsic germanium structures fabricated on a silicon substrate. This direct approach activates the plasmonic resonance of the Ge structures and enables their use as optical antennas up to the mid-infrared spectral range. The optical switching lasts for hundreds of picoseconds until charge recombination redshifts the plasma frequency. The full behavior of the structures is modeled by the electrodynamic response established by an electron-hole plasma in a regular array of antennas.