No abstract

We have investigated the electronic structure of Rashba spin-split quantum wires in a magnetic field. For our numerical calculations, a harmonic confinement was assumed. We find that wire structures with several occupied one-dimensional subbands still exhibit a beating pattern in the magnetoresistance. The wire width turns out to strongly affect the magnetic field values at which nodes occur in the beating pattern. In the limit of narrow wires, the beating pattern would vanish altogether because spin-split subbands become populated equally.

The Rashba spin-orbit coupling in InGaAs/ InP quantum wire structures with a width varying between 1 m and 400 nm is investigated. For all quantum wire structures a clear beating pattern in the oscillations of the magnetoresistance owing to the presence of Rashba spin-orbit coupling is observed. By applying a bias voltage to a gate electrode covering the wires it was possible to control the magnitude of the spin-orbit coupling. For the narrowest wire the effect of the confining potential on the sublevel spectrum could be resolved in the magnetoresistance oscillations. It is found that the node of the beating pattern shifts towards larger magnetic fields with decreasing wire width. The corresponding increase of the Rashba spin-orbit coupling parameter is explained by the effect of the confining potential of the wire.

A novel design for an all-reflective unobscured optical-power zoom (OPZ) objective with a zoom factor of 3 is presented. In contrast to OPZ objectives based on liquid lenses, all-reflective objectives use only reflective elements and are therefore free of chromatic aberrations. Thus, they can be used for a wide spectral range or in combination with image sensors that differ in their spectral characteristics. To avoid a decrease in image contrast encountered in on-axis designs with central obscuration, an unobscured off-axis or "Schiefspiegler" approach is adopted. The effective focal length of the objective is changed by two deformable mirrors, each with one actuator only. The simulated final design shows adequate image quality over the whole zooming range. Before starting the complex and cost-intensive development of deformable mirrors with the size, curvature, and dynamic range needed, the optical design should be evaluated first with respect to the practical achievable optical performance. Therefore, optomechanical setups with ultraprecision-manufactured solid mirrors were realized for three different focal lengths.

Near-infrared (NIR) spectroscopy is a well-established technique for the chemical analysis of organic and inorganic matter. Accordingly, spectroscopic instrumentation of different complexity has been developed and is currently commercially available. However, there are an increasing number of new mobile applications that have come into focus and that cannot be addressed by the existing technology due to size and cost. Therefore, a new miniaturized scanning grating spectrometer for NIR spectroscopy has been developed at Fraunhofer IPMS. It is based on micro–electro–mechanical systems (MEMS) technology, and has been designed to meet the requirements for mobile application, regarding spectral range, resolution, overall size, robustness, and cost. The MEMS spectrometer covers a spectral range from 950 nm to 1900 nm at a resolution of 10 nm. The instrument is extremely small and has a volume of only 2.1 cm3. Therefore, it is well suited for integration, even into a mobile phone. A first sample of the new spectrometer has been manufactured and put into operation. The results of a series of test measurements are in good agreement with the requirements and specifications.