Biomedical subjects

S Knappe

Publications and source records attributed to S Knappe.

5 recordsLinked to original sources

PubMed2006

Compact phase delay technique for increasing the amplitude of coherent population trapping resonances in open Lambda systems.

We propose and demonstrate a novel technique for increasing the amplitude of coherent population trapping (CPT) resonances in open Lambda systems. The technique requires no complex modifications to the conventional CPT setup and is compatible with standard microfabrication processes. The improvement in the CPT resonance amplitude as a function of intensity of the excitation light agrees well with the theory based on ideal open and closed Lambda systems.

Journal Article↗

PubMed2006

Atomic-based stabilization for laser-pumped atomic clocks.

We describe a novel technique for stabilizing frequency shifts in laser-interrogated vapor-cell atomic clocks. The method suppresses frequency shifts due to changes in the laser frequency, intensity, and modulation index as well as atomic vapor density. The clock operating parameters are monitored by using the atoms themselves, rather than by using conventional schemes for laser frequency and cell temperature control. The experiment is realized using a chip-scale atomic clock. The novel atomic-based stabilization approach results in a simpler setup and improved long-term performance.

Journal Article↗

PubMed2006

[Three-dimensional confocal laser scanning microscopy of the corneal nerve structure].

PURPOSE: The aim of this study was the evaluation of a technology for in vivo visualization of distribution and morphology of corneal nerves by means of 3D confocal laser scanning microscopy (3D-CLSM). METHOD: The anterior corneas of four human volunteers were examined by an in-house developed confocal laser scanning microscope based on a commercially available instrument (Heidelberg Retina Tomograph II, Heidelberg Engineering GmbH, Germany). Raw stacks were converted using ImageJ (NIH, USA) for 3D-reconstruction using AMIRA 3.1 (TGS Inc, USA). RESULTS: The spatial arrangement of epithelium, nerves and keratocytes was visualized by in vivo 3D-CLSM. After 3D-reconstruction of volunteers' corneas, volume rendering and selective oblique sections have been done to demonstrate the nerves in the central human cornea. 3D-imaging shows thick nerve bundles rising out of the deeper stroma. The nerves further divide, resulting in fibers that are arranged parallel to Bowman's layer and are partly interconnected. Branches rising up to the superficial cell layer cannot be visualized. Wound healing following refractive surgery can be evaluated. CONCLUSIONS: 3D-CLSM allows in vivo visualization and analysis of the spatial arrangement of the epithelium, nerves and keratocytes of the human cornea. The developed method provides a basis for further studies on the alterations of the cellular arrangement and epithelial innervation in corneal diseases. This may help to clarify gross variations of nerve fiber patterns under various clinical and experimental conditions.

Adult↗

PubMed2005

Atomic vapor cells for chip-scale atomic clocks with improved long-term frequency stability.

A novel technique for microfabricating alkali atom vapor cells is described in which alkali atoms are evaporated into a micromachined cell cavity through a glass nozzle. A cell of interior volume 1 mm3, containing 87Rb and a buffer gas, was made in this way and integrated into an atomic clock based on coherent population trapping. A fractional frequency instability of 6 x 10(-12) at 1000 s of integration was measured. The long-term drift of the F=1, mF=0-->F=2, mF=0 hyperfine frequency of atoms in these cells is below 5 x 10(-11)/day.

Journal Article↗

PubMed2005

[Epidemic keratoconjunctivitis. In vivo images of corneal structures with the confocal Rostocker laser scanning microscope (RLSM)].

PURPOSE: Epidemic keratoconjunctivitis (EKC) is a highly contagious infection caused by adenovirus types 8, 19, and 37. The formation of subepithelial nummular infiltrates may lead to permanent visual disturbance. These infiltrates consist histopathologically of an accumulation of lymphocytes, histiocytes, and fibroblasts. PATIENT AND METHOD: The reasons for the persistence of these nummular infiltrates are not fully understood. We examined a 28-year-old female patient with typical signs of EKC infection clinically and additionally with the RLSM. RESULTS: Nummuli were identified by the RLSM as areas with an accumulation of dendritic cells (supposed to be Langerhans cells) as well as so far unidentified punctiform structures located in the basal cell layer and in the region of the subepithelial nerve plexus. CONCLUSIONS: The RLSM allows us to investigate corneal microstructures in vivo with precise depth localization related to epidemic keratoconjunctivitis. Further investigations may disclose the role of dendritic cells in the pathogenesis of the nummular formation as well as their contribution to the variable persistence of partially threatening vision opacities.

Adult↗