Rolf Brönnimann

Application and reliability of a fiber optical surveillance system for a stay cable bridge

In this paper we report on the application of a fiber optical system for the surveillance of a new stay cable bridge. The novelty of the bridge is the use of cables made of carbon-fiber-reinforced polymer wires. This new concept in bridge construction requires monitoring of the cables to ensure their reliability. The results of an observation period of more than six months during the construction are presented. Tests of the reliability of the fiber optical monitoring system are discussed.

Milling micro-structures using focused ion beams and its application to photonic components

Investigations in micro-structuring optical fibre tips with direct focused ion beam writing will be discussed. The first part considers fundamental aspects and shows relevant experiments to understand and control ion patterning. The second part exemplifies structuring of photonic elements by the fabrication of apertures on an optical fibre tip and the corresponding optical characterizations.

Single-Cell Mass Spectrometry of Metabolites Extracted from Live Cells by Fluidic Force Microscopy

Single-cell metabolite analysis provides valuable information on cellular function and response to external stimuli. While recent advances in mass spectrometry reached the sensitivity required to investigate metabolites in single cells, current methods commonly isolate and sacrifice cells, inflicting a perturbed state and preventing complementary analyses. Here, we propose a two-step approach that combines nondestructive and quantitative withdrawal of intracellular fluid with subpicoliter resolution using fluidic force microscopy, followed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The developed method enabled the detection and identification of 20 metabolites recovered from the cytoplasm of individual HeLa cells. The approach was further validated in 13C-glucose feeding experiments, which showed incorporation of labeled carbon atoms into different metabolites. Metabolite sampling, followed by mass spectrometry measurements, enabled the preservation of the physiological context and the viability of the analyzed cell, providing opportunities for complementary analyses of the cell before, during, and after metabolite analysis.

Simultaneous measurement of NO and NO(2) by dual-wavelength quantum cascade laser spectroscopy.

The concept of a multi-wavelength quantum cascade laser emitting at two or more spectrally well-separated wavelengths is highly appealing for applied spectroscopy, as it allows detecting several species with compact and cost-efficient optical setups. Here we present a practical realization of such a dual-wavelength setup, which is based on a room-temperature quantum cascade laser emitting single-mode at 1600 cm-1 and 1900 cm-1 and is thus well-suited for simultaneous NO and NO2 detection. Operated in a time-division multiplexed mode, our spectrometer reaches detection limits of 0.5 and 1.5 ppb for NO2 and NO, respectively. The performance of the system is validated against the well-established chemiluminescence detection while measuring the NOx emissions on an automotive test-bench, as well as upon monitoring the pollution at a suburban site.

Intermittent operation of QC-lasers for mid-IR spectroscopy with low heat dissipation: tuning characteristics and driving electronics

Intermittent scanning for continuous-wave quantum cascade lasers is proposed along with a custom-built laser driver optimized for such operation. This approach lowers the overall heat dissipation of the laser by dropping its drive current to zero between individual scans and holding a longer pause between scans. This allows packaging cw-QCLs in TO–3 housings with built-in collimating optics, thus reducing cost and footprint of the device. The fully integrated, largely analog, yet flexible laser driver eliminates the need for any external electronics for current modulation, lowers the demands on power supply performance, and allows shaping of the tuning current in a wide range. Optimized ramp shape selection leads to large and nearly linear frequency tuning (>1.5 cm−1). Experimental characterization of the proposed scheme with a QCL emitting at 7.7 μm gave a frequency stability of 3.2×10−5 cm−1 for the laser emission, while a temperature dependence of 2.3×10−4 cm−1/K was observed when the driver electronics was exposed to sudden temperature changes. We show that these characteristics make the driver suitable for high precision trace gas measurements by analyzing methane absorption lines in the respective spectral region.

Resonance Light Scattering in Dye-Aggregates Forming in Dewetting Droplets

Small organic semiconducting molecules assembling into supramolecular J- and H- aggregates have attracted much attention due to outstanding optoelectronic properties. However, their easy and reproducible fabrication is not yet sufficiently developed for industrial applications, except for silver halide photography. Here we present a method based on aggregate precipitation during the phase separation and dewetting of the evaporating dye precursor solution. The smaller the precursor droplets, the more pronounced the J-aggregation. The aggregates cause the films to resonantly scatter incoming light. Because the dye aggregate extinction resonances have narrowest bandwidths, a wavelength selectivity is observed that exceeds the selectivity of localized surface plasmon resonances. The aggregation mechanism can be easily applied to periodically structured substrates, making the method appealing for photonic applications. We demonstrate this point with a 2D grating, where the narrow absorption range of the aggregates leads to wavelength specific (one color only) scattering.

Optimized fabrication of curved surfaces by a FIB for direct focusing with glass fibres

A focused ion beam (FIB) was used to fabricate Fresnel phase lenses on optical fibre tips. The influence of dwell time and the scanning strategy to produce parabolic structures in silicon was investigated, because these parameters have a strong influence on the shape of the fabricated structures. The lens shape was characterized by atomic force microscopy and it was shown that the FIB does not roughen the surfaces. The optical performance of the lenses was characterized by scanning near field optical microscopy (SNOM) and the results were compared to simulations taking into account fabrication imperfections of the Fresnel lenses. At a wavelength of 840 nm a spot size of 740 nm FWHM was achieved.

Long-term monitoring of polarization-mode dispersion of aerial optical cables with respect to line availability

Physical and technical limits become important when trying to increase data transfer rates to tens of gigabits and higher for already installed optical cables. Polarization-mode dispersion (PMD) is one of the crucial transmission constraints, especially for aerial cables exposed to environmental stresses. Optical fibers in the laboratory and three aerial optical fiber cable links across the Swiss alps were characterized with respect to PMD. Long-term measurement results are correlated to weather data along the cables, and predictions regarding line availability are made.

20 Years of Experience with Structural Health Monitoring of Objects with CFRP Components

The application of carbon fiber reinforced polymers (CFRP) in bridge construction was before 1991 unknown. Therefore the bridge owners did not want to rely only on the laboratory experiments made in the 1980ties. They asked for structural health monitoring. This was also in the interest of the involved R&D community. The used devices range from “old fashioned” demec gauges for off-line measurements to classical foil resistance strain gauges, self-sensing systems for unidirectional CFRP wires, and also sophisticated integrated fiber optical sensors with Bragg gratings. In the most important applications different independent systems were used in parallel. Twenty years are for devices which are exposed to outdoor weathering a fairly demanding time span. Therefore the surprisingly high reliability of most of these systems is a largely appreciated result. Applications on post-tensioned reinforced concrete bridges, stay cables, and pretensioned powerline pylons will be discussed.

Sample handler for x-ray tomographic microscopy and image-guided failure assessment

X-ray tomographic microscopy (XTM) yields a three-dimensional data model of an investigated specimen. XTM providing micrometer resolution requires synchrotron light, high resolution area detectors, and a precise sample handler. The sample handler has a height of 270 mm only, is usable for 1μm resolution, and is able to carry loading machines with a weight of up to 20 kg. This allows exposing samples to load between scans for image-guided failure assessment. This system has been used in the XTM end station of the materials science beamline of the Swiss Light Source at the Paul Scherrer Institut.