A simple integrated single-atom detector

We present a reliable and robust integrated fluorescence detector capable of detecting single atoms. The detector consists of a tapered lensed single-mode fiber for precise delivery of excitation light and a multimode fiber to collect the fluorescence. Both are mounted in lithographically defined SU-8 holding structures on an atom chip. Rb87 atoms propagating freely in a magnetic guide are detected with an efficiency of up to 66%, and a signal-to-noise ratio in excess of 100 is obtained for short integration times.Comment: 3 pages, 3 figure

Fabrication of alignment structures for a fiber resonator by use of deep-ultraviolet lithography

We present a novel method to mount and align an optical-fiber-based resonator on the flat surface of an atom chip with ultrahigh precision. The structures for mounting a pair of fibers, which constitute the fiber resonator, are produced by a spin-coated SU-8 photoresist technique by use of deep-UV lithography. The design and production of the SU-8 structures are discussed. From the measured finesses we calculate the coupling loss of the SU-8 structures acting as a kind of fiber splice to be smaller than 0.013 dB.Comment: 4 pages, 3 figure

Single atom detection on an atom chip with integrated optics

The subject of this thesis is the miniaturization and integration of detectors for the detection of single rubidium atoms on an atom chip. For this purpose three different detectors were developed for atom detection by absorption or fluorescence: i) A fluorescence detector was realized by mounting a tapered lensed fiber perpendicular to a collection fiber. ii) An absorption detector was built by placing a multi-mode fiber in-line with a tapered lensed fiber. iii) A tunable cavity detector was built from two single mode fibers mounted on the chip surface. To mount the detectors on the planar surface of the atom chip retaining structures by means of lithographical techniques were developed. Those structures allow a very accurate and stable passive fiber alignment. To test the individual detectors an atomic ensemble of thermal rubidium atoms was prepared in a magneto-optical trap. Then the atoms were transferred into magnetic micro-traps of the atom chip and were guided to one of the detectors. Each integrated detector has been evaluated by several characterization measurements. With the fluorescence detector the highest single atom detection efficiency of 54\% was attained. Thereby it was possible to perform quantitative measurements for the magnetically guided atoms on a single atom level and to study fundamental properties of the confined atoms

Schallfeldformung zur Reduzierung der Behandlungszeit bei der Therapie mit hochenergetischen fokussierten Ultraschallwellen

Die Therapie mit hochenergetischen fokussierten Ultraschallwellen (HIFU, high intensity focused ultrasound) ist eine minimal invasive Methode, Tumorgewebe lokal thermisch zu zerstören. Als Ultraschallquellen werden meist hoch fokussierende Ultraschallwandler verwendet, die nur geringe Ablationsraten zulassen, was bei großen Tumoren zu langen Behandlungszeiten führen kann. Gegenstand dieser Arbeit war es, Möglichkeiten zur Reduktion der Therapiezeit zu untersuchen. Zunächst wurden mittels mathematischer Simulationen Ultraschall-Vorsatzlinsen zur Modifikation eines gegebenen fokussierten Schallfeldes entwickelt. Die zwei besten Linsen wurden aus Polystyrol angefertigt und experimentell untersucht. Hierzu diente ein neues, im Rahmen dieser Arbeit entwickeltes, gewebeähnliches Ultraschallphantom aus einer mit Hühnereiweiß dotierten Polyacrylamidmatrix. In einem weiteren Schritt wurde für eine gegebene klinische HIFU-Therapieeinheit mittels Simulationsrechungen ein optimierter Phased Array Ultraschallwandler konstruiert. Sowohl in den Simulationen als auch experimentell konnte gezeigt werden, dass mit den entwickelten Ultraschalllinsen die Ablationszeiten bis auf ein Fünftel reduziert werden können. Das entwickelte Ultraschallphantom ist transparent und zeigt bei Temperaturen über 67°C sichtbare weiße Koagulationen. Die theoretischen Untersuchungen zum Aufbau eines Phased Array Ultraschallwandlers (Durchmesser 100 mm, Brennweite 88 mm) haben gezeigt, dass eine randomisierte Elementanordnung von 217 Einzelelementen mit einem Elementdurchmesser von 4,5 mm bei einer Frequenz von 1,5 MHz für die Therapie von Mammatumoren in der vorgegebenen Therapieeinheit optimal sind. Die in dieser Arbeit entwickelten Ultraschalllinsen werden zukünftig zur Beschleunigung der HIFU-Therapie von Tumoren der Mamma klinisch eingesetzt. Mit dem transparenten Ultraschallphantom ist ein standardisiertes Hilfsmittel geschaffen worden, das den Vergleich von Simulation und Experiment deutlich vereinfacht. Eine Realisierung des konstruierten Phased Array Wandlers würde die HIFU-Therapieeinheit noch weiter flexibilisieren

A microfabricated surface ion trap on a high-finesse optical mirror

A novel approach to optics integration in ion traps is demonstrated based on a surface electrode ion trap that is microfabricated on top of a dielectric mirror. Additional optical losses due to fabrication are found to be as low as 80 ppm for light at 422 nm. The integrated mirror is used to demonstrate light collection from, and imaging of, a single 88 Sr+ ion trapped $169\pm4 \mu$m above the mirror.Comment: 4 pages, 3 figure

A single atom detector integrated on an atom chip: fabrication, characterization and application

We describe a robust and reliable fluorescence detector for single atoms that is fully integrated into an atom chip. The detector allows spectrally and spatially selective detection of atoms, reaching a single atom detection efficiency of 66%. It consists of a tapered lensed single-mode fiber for precise delivery of excitation light and a multi-mode fiber to collect the fluorescence. The fibers are mounted in lithographically defined holding structures on the atom chip. Neutral 87Rb atoms propagating freely in a magnetic guide are detected and the noise of their fluorescence emission is analyzed. The variance of the photon distribution allows to determine the number of detected photons / atom and from there the atom detection efficiency. The second order intensity correlation function of the fluorescence shows near-perfect photon anti-bunching and signs of damped Rabi-oscillations. With simple improvements one can boost the detection efficiency to > 95%.Comment: 24 pages, 11 figure

MSAViewer:interactive JavaScript visualization of multiple sequence alignments

Summary: The MSAViewer is a quick and easy visualization and analysis JavaScript component for Multiple Sequence Alignment data of any size. Core features include interactive navigation through the alignment, application of popular color schemes, sorting, selecting and filtering. The MSAViewer is ‘web ready’: written entirely in JavaScript, compatible with modern web browsers and does not require any specialized software. The MSAViewer is part of the BioJS collection of components. Availability and Implementation: The MSAViewer is released as open source software under the Boost Software License 1.0. Documentation, source code and the viewer are available at http://msa.biojs.net/. Supplementary information: Supplementary data are available at Bioinformatics online. Contact: [email protected]

Clouds, shadows, or twilight? Mayfly nymphs recognise the difference

1. We examined the relative changes in light intensity that initiate night-time locomotor activity changes in nymphs of the mayfly, Stenonema modestum (Heptageniidae). Tests were carried out in a laboratory stream to examine the hypothesis that nymphs increase their locomotion in response to the large and sustained reductions in relative light intensity that take place during twilight but not to short-term daytime light fluctuations or a minimum light intensity threshold. Ambient light intensity was reduced over a range of values representative of evening twilight. Light was reduced over the same range of intensities either continuously or in discrete intervals while at the same time nymph activity on unglazed tile substrata was video recorded. 2. Nymphs increased their locomotor activity during darkness in response to large, sustained relative light decreases, but not in response to short-term, interrupted periods of light decrease. Nymphs did not recognise darkness unless an adequate light stimulus, such as large and sustained relative decrease in light intensity, had taken place. 3. We show that nymphs perceive light change over time and respond only after a lengthy period of accumulation of light stimulus. The response is much lengthier than reported for other aquatic organisms and is highly adaptive to heterogeneous stream environments

Interval scheduling maximizing minimum coverage

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