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•The melamine distribution in polyester/melamine coatings has been studied.•Depth resolved quantification of the melamine crosslinker was achieved.•Free standing films behave ...differently than coatings applied on galvanized steel.•The highest melamine concentration is expected in the surface near region of a coating.•A new qualitative model on the melamine distribution is proposed.
The depth distribution of melamine in polyester-based coatings was investigated by XPS (X-ray photoelectron spectroscopy) as well as Raman analysis on cryo-ultra-low-angle microtome (cryo-ULAM) prepared coatings on hot dip galvanized (HDG) steel panels. Additionally, free standing films were analyzed on the air/coating and the coating/substrate interfaces: for polyester/melamine ratios ≤20wt.% the melamine concentration was equal on both sides of free films, which is in accordance with literature. This finding could not be confirmed for the coatings applied on HDG steel panels that revealed a higher amount of melamine in the surface-near region. In addition various types of non-linear melamine concentration gradients have been detected over depth by XPS as well as Raman spectroscopy. This behavior was confirmed for all types of coatings irrespective of binder chemistry and curing temperatures in the range of 220–260°C. Whereas previous studies have mainly focused on higher melamine concentration where gradient properties are more pronounced, this work tries to fills the gap towards lower melamine contents, which are of greater relevance for industrial coatings. According to these results, a qualitative model on the melamine distribution has been established, which explains the observed non-linear gradients on the basis of transport phenomena and crosslinking kinetics within the curing process. This model is also in agreement with experimental findings from previous works.
The upcoming European design study 'Einstein gravitational-wave Telescope' represents the first step towards a substantial, international effort for the design of a third-generation interferometric ...gravitational wave detector. It is generally believed that third-generation instruments might not be installed into existing infrastructures but will provoke a new search for optimal detector sites. Consequently, the detector design could be subject to fewer constraints than the on-going design of the second-generation instruments. In particular, it will be prudent to investigate alternatives to the traditional L-shaped Michelson interferometer. In this paper, we review an old proposal to use three Michelson interferometers in a triangular configuration. We use this example of a triple Michelson interferometer to clarify the terminology and will put this idea into the context of more recent research on interferometer technologies. Furthermore, the benefits of a triangular detector will be used to motivate this design as a good starting point for a more detailed research effort towards a third-generation gravitational-wave detector.
The Sagnac speed metre topology has been identified as a promising technique to reduce quantum back-action in gravitational-wave interferometers. However, imbalance of the main beamsplitter has been ...shown to increase the coupling of laser noise to the detection port, thus reducing the quantum noise superiority of the speed metre, compared to conventional approaches, in particular at low frequencies. In this paper, we show that by implementing a balanced homodyne readout scheme with a suitable choice of the point from which the local oscillator (LO) is derived, the excess laser noise contribution is partly compensated, and the resulting speed metre can be more sensitive than state-of-the-art position metres. This is achieved by picking-off the LO from either the reflection port of the interferometer or the anti-reflective coating surface of the main beamsplitter. We show that either approach relaxes the relative intensity noise (RIN) requirement of the input laser. For example, for a beam splitter imbalance of 0.1% in the Glasgow speed metre proof of concept experiment, the RIN requirement at frequency of 100 Hz decreases from 4 × 10 − 10 Hz to 4 × 10 − 7 Hz , moving the RIN requirement from a value that is hard to achieve in practice, to one which is routinely obtained.
We apply the Collins-Huygens integral to analytically describe propagation of a doughnut beam generated by a spiral phase plate. Measured beam profiles in free space and through an ABCD-lens system ...illustrate excellent agreement with theory. Applications range from the creation of optical beams with angular momentum to microscopy to trapping neutral atoms. The method extends to other beam shaping components, too.
All first-generation large-scale gravitational wave detectors are operated at the dark fringe and use a heterodyne readout employing radio frequency (RF) modulation-demodulation techniques. However, ...the experience in the currently running interferometers reveals several problems connected with a heterodyne readout, of which phase noise of the RF modulation is the most serious one. A homodyne detection scheme (DC-readout), using the highly stabilized and filtered carrier light as a local oscillator for the readout, is considered to be a favourable alternative. Recently a DC-readout scheme has been implemented on the GEO 600 detector. We describe the results of first measurements and give a comparison of the performance achieved with homodyne and heterodyne readout. The implications of the combined use of DC-readout and signal recycling are considered.
The uptake of carbon nanotubes (CNTs) by mammalian cells and their distribution within cells is being widely studied in recent years due to their increasing use for biomedical purposes. The two main ...imaging techniques used are confocal fluorescence microscopy and transmission electron microscopy (TEM). The former, however, requires labeling of the CNTs with fluorescent dyes, while the latter is a work-intensive technique that is unsuitable for in situ bio-imaging. Raman spectroscopy, on the other hand, presents a direct, straightforward and label-free alternative. Confocal Raman microscopy can be used to image the CNTs inside cells, exploiting the strong Raman signal connected to different vibrational modes of the nanotubes. In addition, cellular components, such as the endoplasmic reticulum and the nucleus, can be mapped. We first validate our method by showing that only when using the CNTs' G band for intracellular mapping accurate results can be obtained, as mapping of the radial breathing mode (RBM) only shows a small fraction of CNTs. We then take a closer look at the exact localization of the nanotubes inside cells after folate receptor-mediated endocytosis and show that, after 8-10 h incubation, the majority of CNTs are localized around the nucleus. In summary, Raman imaging has enormous potential for imaging CNTs inside cells, which is yet to be fully realized.
Speedmeters are known to be quantum non-demolition devices and, by potentially providing sensitivity beyond the standard quantum limit, become interesting for third generation gravitational wave ...detectors. Here we introduce a new configuration, the sloshing-Sagnac interferometer, and compare it to the more established ring-Sagnac interferometer. The sloshing-Sagnac interferometer is designed to provide improved quantum noise limited sensitivity and lower coating thermal noise than standard position meter interferometers employed in current gravitational wave detectors. We compare the quantum noise limited sensitivity of the ring-Sagnac and the sloshing-Sagnac interferometers, in the frequency range, from 5 Hz to 100 Hz, where they provide the greatest potential benefit. We evaluate the improvement in terms of the unweighted noise reduction below the standard quantum limit, and by finding the range up to which binary black hole inspirals may be observed. The sloshing-Sagnac was found to give approximately similar or better sensitivity than the ring-Sagnac in all cases. We also show that by eliminating the requirement for maximally-reflecting cavity end mirrors with correspondingly-thick multi-layer coatings, coating noise can be reduced by a factor of approximately 2.2 compared to conventional interferometers.
A pivotal aspect in increasing the sensitivity of the Advanced LIGO detectors to allow the first gravitational wave detection, GW150914, was the installation of the monolithic fused silica ...suspensions. The 40 kg test mass suspended by four 400 μm fused silica fibres lowers the thermal noise as compared to initial LIGO. There is a desire for the use of thinner fibres to suspend smaller optics for other experiments of interest to the gravitational wave community that the current aLIGO fibre pulling machine is not capable of. We present here an overview of a new CO2 laser-based micron scale diameter fibre pulling machine developed at the University of Glasgow, based on the principals of our current aLIGO fibre pulling machine. We also discuss the upgraded fibre characterisation apparatus for dimensional and strength testing. It was found that fibres with a minimum diameter between 7.6 and 9.3 μm had an average breaking stress of 2.7 GPa and a Young's modulus value of 63.3 GPa, which is lower than the accepted bulk value of 72 GPa. Fibres with an average diameter between 13.2 and 17.8 μm had higher breaking stress and Young's modulus values ranging between 3.7-4.0 GPa and 71.8-75.9 GPa, respectively.
Optical rigidity will play an important role in future generations of gravitational wave (GW) interferometers which employ high laser power in order to reach and exceed the standard quantum limit. ...Several experiments have demonstrated the optical spring effect for very low weight mirror masses. In this paper we extend this to a mass and frequency regime more directly applicable to GW detectors. Using a end mirror mass we demonstrate an optical spring resonant at and a stiffness of 9.4 ×105 N m−1. The to mass regime may also be useful for the application as a readout mirror for optical bar or optical lever configurations.
Brownian noise of dielectric mirror coatings is expected to be one of the limiting noise sources, at the peak sensitivity, of next generation ground based interferometric gravitational wave (GW) ...detectors. The use of higher-order Laguerre-Gauss (LG) beams has been suggested to reduce the effect of coating thermal noise in future generations of gravitational wave detectors. In this paper we describe the first test of interferometry with higher-order LG beams in an environment similar to a full-scale gravitational wave detector. We compare the interferometric performance of higher-order LG modes and the fundamental mode beams, injected into a 10 m long suspended cavity that features a finesse of 612, a value chosen to be typical of future gravitational wave detectors. We found that the expected mode degeneracy of the injected LG3, 3 beam was resolved into a multiple peak structure, and that the cavity length control signal featured several nearby zero crossings. The break up of the mode degeneracy is due to an astigmatism (defined as |Rcy − Rcx|) of 5.25 ± 0.5 cm on one of our cavity mirrors with a radius of curvature (Rc) of 15 m. This observation agrees well with numerical simulations developed with the FINESSE software. We also report on how these higher-order mode beams respond to the misalignment and mode mismatch present in our 10 m cavity. In general we found the LG3, 3 beam to be considerably more susceptible to astigmatism and mode mismatch than a conventional fundamental mode beam. Therefore the potential application of higher-order Laguerre-Gauss beams in future gravitational wave detectors will impose much more stringent requirements on both mode matching and mirror astigmatism.
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