Mid-infrared (MIR) photonics demands highly confined optical fields to obtain efficient interaction between long-wavelength light and nanomaterials. Surface polaritons excited on polar semiconductor and metallic material interfaces exhibit near-fields localized on subwavelength scales. However, realizing a stronger field concentration in a cavity with a high quality (Q) factor and a small mode volume is still challenging in the MIR region. This study reports MIR field concentration of surface phonon polaritons (SPhPs) using planar circular cavities with a high Q factor of ∼150. The cavities are fabricated on a thin film of the phase change material Ge3Sb2Te6 (GST) deposited on a silicon carbide (SiC) substrate. Scattering-type scanning near-field optical microscopy visualizes the near-field distribution on the samples and confirms directly that the SPhP field is strongly concentrated at the center of the centrosymmetric cavities. The smallest concentrated field size is 220 nm in diameter which corresponds to 1/50 of the wavelength of the incident light that is far below the diffraction limit. The thin GST film enhances the SPhP confinement, and it is used to switch the confinement off by tuning the cavity resonance induced by the phase change from the amorphous to the crystalline phase. This subwavelength and switchable field concentration within a high-Q polariton cavity has the potential to greatly enhance the light-matter interaction for molecular sensing and emission enhancement in MIR systems.

In diesem Beitrag wird ein "Chirp"-Oberflächennormal vorgestellt. Es ist dafür vorgesehen, mit einer Serie von verschiedenen Ortsfrequenzen das Übertragungsverhalten von Oberflächenmessgeräten zu testen. Die Topografie des Normals enthält eine abgestufte Folge von Sinuswellen, deren Abstände, Steigungen und Krümmungen durch den Synthese-und Fertigungsprozess genau bekannt sind. Die Oberfläche des Normals wird durch einen Diamant-Drehprozess hergestellt. Bei der Erzeugung der NC-Steuerdaten wird mittels morphologischer Operationen der Einfluss der Werkzeuggeometrie berücksichtigt. Erste Ergebnisse von Messungen am Chirp-Normal mit Interferenzmikroskopen und Tastschnittgeräten werden gezeigt.In this article a chirp-calibration standard is presented. It is intended to test the function transfer of surface measuring instruments by a series of different space scaled frequencies. The standard contains a sequence of sinusoidal waves, the distance, slopes and curvatures of which are well known from the design and the manufacturing process. The surface of the specimen is manufactured by a single diamond turning process. The control data take into account the influence of the cutting tool by morphological operations. First results of measurements on the chirp standard by both a contact stylus instrument and an interference microscope are presented.

BackgroundDespite the high frequency of cognitive impairment in multiple sclerosis, its assessment has not gained entrance into clinical routine yet, due to lack of time-saving and suitable tests for patients with multiple sclerosis.ObjectiveThe aim of the study was to compare the paradigm of visual search with neuropsychological standard tests, in order to identify the test that discriminates best between patients with multiple sclerosis and healthy individuals concerning cognitive functions, without being susceptible to practice effects. MethodsPatients with relapsing remitting multiple sclerosis (n = 38) and age-and gender-matched healthy individuals (n = 40) were tested with common neuropsychological tests and a computer-based visual search task, whereby a target stimulus has to be detected amongst distracting stimuli on a touch screen. Twenty-eight of the healthy individuals were re-tested in order to determine potential practice effects.ResultsMean reaction time reflecting visual attention and movement time indicating motor execution in the visual search task discriminated best between healthy individuals and patients with multiple sclerosis, without practice effects. ConclusionsVisual search is a promising instrument for the assessment of cognitive functions and potentially cognitive changes in patients with multiple sclerosis thanks to its good discriminatory power and insusceptibility to practice effects.

Doped semiconductor nanostructures are interesting for the fabrication of nanoscale electronic and photonic devices. Here, we use scattering-type scanning near-field optical microscopy (s-SNOM) to characterize axial carrier density gradients in phosphorus-doped silicon nanowires. We quantitatively determine the carrier density and length of the doped segment as well as the functional form of the charge carrier gradient in the transition region between doped and nominally undoped segments. These measurements are enabled by understanding and accounting for the influence of the native oxide on the near-field optical contrasts in the transition region. Our results are supported by correlative energy dispersive X-ray spectroscopy (EDS) measurements. This work demonstrates the ability of s-SNOM to directly probe nanoscale charge carrier density transitions through thin surface layers, a capability that is important for a variety of doped semiconductor systems.

Phase Change Materials (PCM) show two stable states in the solid phase with significantly different optical and electronic properties. They can be switched reversibly between those two states and are promising candidates for future non-volatile memory applications. The development of phase change devices demands characterization tools, yielding information about the switching process at high spatial resolution. Scattering-type Scanning Near-field Optical Microscopy (s-SNOM) allows for spectroscopic analyses of the different optical properties of the PCMs on the nm-scale. By correlating the optical s-SNOM images with transmission electron microscopy images of the same sample, we unambiguously demonstrate the correlation of the infrared optical contrast with the structural state of the phase change material. The investigated sample consists of sandwiched amorphous and crystalline regions of Ag4 In3 Sb67 Te26 below a 100 nm thick (ZnS)80 - (SiO2)20 capping layer. Our resul ts demonstrate the sensitivity of s-SNOM to small dielectric near-field contrasts even below a comparably thick capping layer (100 nm)