Multiple-beam Fringe Tracking for the VLTI

ESO’s program of second generation VLT and VLTI instrumentation comprises (i) 4 approved instruments already in development (X-Shooter, KMOS, MUSE and SPHERE), (ii) up to 3 second generation VLTI instruments whose Phase A studies were recently completed and (iii) tbd additional second generation instruments whose selection prompted this Workshop. The resources provisionally included for additional VLT instruments in ESO’s future planning are comparable to those allocated to those already approved.

We report on the development of a very simple and inexpensive sensor device based on an inductance coil connected to a high-frequency electric field generator. The working principle of this sensor is as follows: liquid sample in a plastic tube is placed inside the inductance coil as its core and this core changes the properties of high-frequency electric current passing through the coil; these changes depend on sample conductivity, dielectric constant, magnetic properties, and capacitance. The electric signal registered after the coil represents a kind of a spectrum that can be effectively treated with chemometric tools. Our studies have shown that such a sensor can be used to distinguish between substances with different physical and chemical properties; different concentrations of ions in aqueous solutions with a linear response in a broad concentration range from 10-3 M to 10-1 M; can quantify the fat content in milk and cream samples with about 2% accuracy; and can distinguish between bacterial cultures and cell line cultures. The measurements are very fast and contactless, and the results show good promise for developing a number of applications of this sensor system.

Exo-zodiacal dust, exozodi for short, is warm (~300K) or hot (up to ~2000K) dust found in the inner regions of planetary systems around main sequence stars. In analogy to our own zodiacal dust, it may be located in or near the habitable zone or closer in, down to the dust sublimation distance. The study of the properties, distribution, and evolution of exozodis can inform about the architecture and dynamics of the innermost regions of planetary systems, close to their habitable zones. On the other hand, the presence of large amounts of exo-zodiacal dust may be an obstacle for future space missions aiming to image Earth-like exoplanets. The dust can be the most luminous component of extrasolar planetary systems, but predominantly emits in the near- to mid-infrared where it is outshone by the host star. Interferometry provides a unique method of separating the dusty from the stellar emission. We discuss the prospects of exozodi observations with the next generation VLTI instruments and summarize critical instrument specifications.

The Galactic Centre at infrared wavelengths: towards the highest spatial resolution

We developed a novel strategy for fabrication of microfluidic paper-based analytical devices (μPADs) by selective wet etching of hydrophobic filter paper using a paper mask having a specific design. The fabrication process consists of two steps. First, the hydrophilic filter paper was patterned hydrophobic by using trimethoxyoctadecylsilane (TMOS) solution as the patterning agent. Next, a paper mask penetrated with NaOH solution (containing 30% glycerol) was aligned onto the hydrophobic filter paper, allowing the etching of the silanized filter paper by the etching reagent. The masked region turned highly hydrophilic whereas the unmasked region remains highly hydrophobic. Thus, hydrophilic channels, reservoirs, and detection zones were generated and delimited by the hydrophobic barriers. The effects of some factors including TMOS concentration, etching temperature, etching time, and NaOH concentration on fabrication of μPAD were studied. Being free of any expensive equipment, metal mask and expensive reagents, this rapid, simple, and cost-effective method could be used to fabricate μPAD by untrained personnel with minimum cost. A flower-shaped μPAD fabricated by this presented method was applied to the glucose assay in artificial urine samples with good performance, indicating its feasibility as a quantitative analysis device. We believe that this method would be very attractive to the development of simple microfluidic devices for point-of-care applications in clinical diagnostics, food safety, and environmental protection.

Mercury ion is a highly toxic anthropogenic pollutants and has serious well-known effects on human. There is an ever-growing demand for convenient detection of mercury driven contaminants in environment, including coastal seawater. However, most of the reported methods are instrument-based and are not easy for portable detection. Our protocol described an efficient Digital Microfluidics method for detecting mercury in coastal seawater samples. It combined the miniaturization/automation potential of digital microfluidics and the sensitivity of fluorescence probe. To overcome a potential risk of driven failure, induced by diversity ion ingredients in seawater, a feedback control loop was included into control system. The method showed satisfied stability and selectivity in Hg sensing under high salinity condition, with the sensitivity of Hg2+ at the parts-per-billion level and total testing time of less than 20 s. With the advantages of being fast, amenable to automation and low cost, this protocol is promising for the formation of simple and rapid sensor device, especially for a routine monitoring and emergency detection of Hg/or other metals in coastal waters.

The resonant modes in a low contrast grating-waveguide structure with a larger aspect ratio possesses unique characteristics, observed under theoretical investigations. Subsequently, a photoresist grating with similar dimensions is realized over a dielectric waveguide to experimentally observe the resonant guided modes (GMR) and cavity modes (CM). In particular, the cavity mode exhibits remarkable characteristics of high sensitivity towards cover index variation, thus with a probable application for environmental index monitoring. In addition, the waveguide-supported GMR mode is negligibly sensitive and may serve as a reference line for such sensing experiments. The spectral responses analyzed in sugar solution with different concentrations as analytes demonstrate a high bulk sensitivity of ~300 nm/RIU in the visible spectrum. Thus, the study opens up possibilities of using optimized grating-based geometry for designing simple yet highly-sensitive handheld sensor devices.

Manganese oxide based screen-printed sensor for xenoestrogens detection

In this study a direct immunosensor for heart-type fatty acid binding protein (FABP) based on surface plasmon resonance spectroscopy (SPRS) is presented. FABP can be used as a heart infarction marker in clinical diagnostics. The development of a simple and cheap direct optical sensor device is reported in this paper as well as immobilization procedures and optimization of the measuring conditions. The correct working of the SPRS device is controlled by comparing the signals with theoretical calculated values. Two different immunoassay techniques were optimized for a sensitive FABP-analysis. The competitive immunoassay was superior to the sandwich configuration as it had a lower detection limit (100 ng/ml), needed less antibodies and could be carried out in one step.

A simple, broadly responsive detector array, based on polymer-carbon black composites that can detect, classify, and quantify various vapors and vapor mixtures is described. The individual detector elements of the array are constructed from films consisting of carbon black particles dispersed into insulating organic polymers. The carbon black provides an electrically conductive network in the films, whereas the different organic polymers are the source of chemical diversity between elements in the detector array. Swelling of the polymer upon exposure to a vapor increases the electrical resistance of the film by disrupting the conductive network of carbon black particles, thereby providing a simple means for monitoring the presence of a vapor. The dc electrical resistance change of an individual composite is shown to be consistent with the predictions of percolation theory. The differing gas-solid partition coefficients between vapor analytes for the various polymers of the detector array produce a characteristic pattern of resistance changes for each analyte. The response of these detectors is linear with variations in analyte concentration, allowing quantification as well as identification of a test analyte. This type of detector array can be used to discriminate different classes of analyte molecules (such as aromatics from alcohols) as well as those within a particular class (such as benzene from toluene and methanol from ethanol). Additionally, by using polymers with chiral subunits, enantiomerically different vapors can be discriminated. Principle component data analysis is used to identify and quantify airborne analytes and the relative compositions of simple gas mixtures. Integration of the electrical resistance signals with data analysis software has made sensing and analysis functions possible in a compact, low-power, simple vapor sensor device.

An innovative continuous type liquid level monitoring system constructed by using a new class of sensor, viz., pulsating sensor, is presented. This device is of industrial grade and it is exclusively used for level monitoring of any non conducting liquid. This instrument of unique design is suitable for high resolution online monitoring of oil level in dashpots of a sodium-cooled fast breeder reactor. The sensing probe is of capacitance type robust probe consisting of a number of rectangular mirror polished stainless steel (SS-304) plates separated with uniform gaps. The performance of this novel instrument has been thoroughly investigated. The precision, sensitivity, response time, and the lowest detection limit in measurement using this device are <0.01 mm, ∼100 Hz/mm, ∼1 s, and ∼0.03 mm, respectively. The influence of temperature on liquid level is studied and the temperature compensation is provided in the instrument. The instrument qualified all recommended tests, such as environmental, electromagnetic interference and electromagnetic compatibility, and seismic tests prior to its deployment in nuclear reactor. With the evolution of this level measurement approach, it is possible to provide dashpot oil level sensors in fast breeder reactor for the first time for continuous measurement of oil level in dashpots of Control & Safety Rod Drive Mechanism during reactor operation.

The Ka-Band Radar Interferometer (KaRIn) instrument on the Surface Water and Ocean Topography (SWOT) mission is a single-pass synthetic aperture radar (SAR) interferometer tasked with, among others, measuring ocean topography to within a few centimeters over kilometer scale resolutions. A SAR interferometer relies on very precise phase difference measurements between two spatially distant antennas to estimate topography. Multipath phase caused by unintended scattering off the spacecraft structure is a known error source for radar interferometers and takes up a significant portion of the KaRIn error budget. This paper outlines some analytical multipath models that were used for instrument design, performance analysis and mitigation of the multipath signal.

The VLTI Data Flow Operations consist in monitoring the performance of the different VLTI instruments offered to the community, in verifying the quality of the calibration and scientific data and their associated products. Since the beginning of MIDI (April 2004) and AMBER (October 2005) Service Mode Operations, scientific as well as calibration data have been accumulated to monitor the instruments and the quality of the observations on different time scales and under different conditions or system configurations. In this presentation, we will describe the Quality Control procedures and give some statistics and results on the different parameters used for instrument monitoring for time scales from hours to years in the case of MIDI. We will show that this includes parameters extracted directly from the instruments (Instrumental Transfer Function, Flux stability, Image Quality, Detector stability...) and parameters extracted from some of the sub-systems associated to the instruments (Adaptive Optics, telescopes used...). We will discuss the development of the monitoring of the instruments once more instrument modes or sub-systems such as PRIMA are offered to the community.

We present the installed and fully operational beam stabilization and fiber injection subsystem feeding the 2nd generation VLTI instrument GRAVITY. The interferometer GRAVITY requires an unprecedented stability of the VLTI optical train to achieve micro-arcsecond astrometry. For this purpose, GRAVITY contains four fiber coupler units, one per telescope. Each unit is equipped with actuators to stabilize the telescope beam in terms of tilt and lateral pupil displacement, to rotate the field, to adjust the polarization and to compensate atmospheric piston. A special roof-prism offers the possibility of on-axis as well as off-axis fringe tracking without changing the optical train. We describe the assembly, integration and alignment and the resulting optical quality and performance of the individual units. Finally, we present the closed-loop performance of the tip-tilt and pupil tracking achieved with the final systems in the lab.

Operating on 6 interferometric baselines, i.e. using all 4 UTs, the 2nd generation VLTI instrument GRAVITY will deliver narrow angle astrometry with 10μas accuracy at the infrared K-band. Within the international GRAVITY consortium, the Cologne institute is responsible for the development and construction of the two spectrometers: one for the science object, and one for the fringe tracking object. Optically two individual components, both spectrometers are two separate units with their own housing and interfaces inside the vacuum vessel of GRAVITY. The general design of the spectrometers, however, is similar. The optical layout is separated into beam collimator (with integrated optics and metrology laser injection) and camera system (with detector, dispersive element, & Wollaston filter wheel). Mechanically, this transfers to two regions which are separated by a solid baffle wall incorporating the blocking filter for the metrology Laser wavelength. The optical subunits are mounted in individual rigid tubes which pay respect to the individual shape, size and thermal expansion of the lenses. For a minimized thermal background, the spectrometers are actively cooled down to an operating temperature of 80K in the ambient temperature environment of the GRAVITY vacuum dewar. The integrated optics beam combiner and the metrology laser injection, which are operated at 200/240K, are mounted thermally isolated to the cold housing of the spectrometers. The optical design has shown that the alignment of the detector is crucial to the performance of the spectrometers. Therefore, in addition to four wheel mechanisms, six cryogenic positioning mechanisms are included in the mechanical design of the detector mount.