134 research outputs found
Mapping the optical absorption of a substrate-transferred crystalline AlGaAs coating at 1.5 µm
No full textThe sensitivity of 2nd and 3rd generations of interferometric gravitational wave detectors will be limited by thermal noise of the test-mass mirrors and highly reflective coatings. Recently developed crystalline coatings show a promising thermal noise reduction compared to presently used amorphous coatings. However, stringent requirements apply to the optical properties of the coatings as well. We have mapped the optical absorption of a crystalline AlGaAs coating which is optimized for high reflectivity for a wavelength of 1064nm. The absorption was measured at 1550nm where the coating stack transmits approximately 70% of the laser light. The measured absorption was lower than (30.2 +/- 11.1)ppm which is equivalent to (3.6 +/- 1.3)ppm for a coating stack that is highly reflective at 1530nm. While this is a very promising low absorption result for alternative low--loss coating materials, further work will be necessary to reach the requirements of <1ppm for future gravitational wave detectors.
Jessica Steinlechner, Iain W Martin, Angus Bell, Garrett Cole, Jim Hough, Steven Penn, Sheila Rowan, Sebastian Steinlechne
Squeezed Light at 2128 nm for future Gravitational-Wave Detectors
No full textSince the first detection of gravitational waves in 2015, the field has been developing to gravitational-wave astronomy with multi-messenger detections and event statistics. Noise sources need to be reduced further to increase the detection range and to get more information about the detected events. In current observatories, coating Brownian noise is the dominant noise source around 100 Hz. To avoid this thermal noise source, the test masses in future gravitational-wave observatories (GWOs) should be cooled to cryogenic temperatures. The mechanical properties of the currently used fused silica worsen at lower temperatures, and therefore the use of crystalline silicon as test mass material is considered, together with amorphous silicon-based coatings. However, this requires a change of the laser wavelength from 1064 nm to around 2 µm. Then, the only remaining noise source in the mid-range and at higher frequencies is quantum noise. Therefore, all technologies for the new wavelength are investigated at a high priority.
This thesis demonstrates a squeezed light source at 1064 nm via wavelength-doubling, where a Nd:YAG nonplanar ring oscillator (NPRO) laser at 1064 nm is used to provide ultra-stable laser light for interferometry. An external conversion efficiency of (87.1±0.4)% (internal 93 %) could be achieved at a pump power of 52 mW. Adapting the conversion scheme to higher laser power might avoid the need of 2 µm laser amplifiers. The NPRO lasers were highly optimized over decades to reach the technological requirements of power stability, amplitude and phase noise. Available lasers around 2 µm do not yet reach the required performance level, but are currently under research. Using squeezed light, the uncertainty of the light field is reduced to (7.2±0.2)dB below shot noise, mainly limited by the quantum efficiency of (92±3)dB of available photodiodes. As part of the technology development two digital control systems were developed which are used for stabilization of cavities (NQontrol) and crystal temperatures (Raspitemp). NQontrol is an open source digital control system that can control eight channels simultaneously, providing complex loop shaping abilities and high flexibility to adapt the system for different needs. Raspitemp is a modular digital temperature control system which can control up to 20 temperatures combined with a high accuracy of <10 mK.
To reach the aimed squeezing level of 10 dB for the next-generation GWOs, the overall optical losses in the interferometer and the detection have to be below 10 %, requiring photodiodes with a quantum efficiency of 99 %. The novel approach of combining optical-parametric down-conversion with the creation of squeezed states is considered as a candidate for next-generation GWOs such as LIGO Voyager and the low-frequency part of the Einstein Telescope
Search for Eccentric Binary Black Hole Mergers with Advanced LIGO and Advanced Virgo during Their First and Second Observing Runs
No full textWhen formed through dynamical interactions, stellar-mass binary black holes (BBHs) may retain eccentric orbits (e > 0.1 at 10 Hz) detectable by ground-based gravitational-wave detectors. Eccentricity can therefore be used to differentiate dynamically formed binaries from isolated BBH mergers. Current template-based gravitational-wave searches do not use waveform models associated with eccentric orbits, rendering the search less efficient for eccentric binary systems. Here we present the results of a search for BBH mergers that inspiral in eccentric orbits using data from the first and second observing runs (O1 and O2) of Advanced LIGO and Advanced Virgo. We carried out the search with the coherent WaveBurst algorithm, which uses minimal assumptions on the signal morphology and does not rely on binary waveform templates. We show that it is sensitive to binary mergers with a detection range that is weakly dependent on eccentricity for all bound systems. Our search did not identify any new binary merger candidates. We interpret these results in light of eccentric binary formation models. We rule out formation channels with rates greater than or similar to 100 Gpc(-3) yr(-1) for e > 0.1, assuming a black hole mass spectrum with a power-law index less than or similar to 2.</p
Quantum metrology with squeezed and entangled light for the detection of gravitational waves
No full text[no abstract
Über den diagnostischen Mehrwert von Antwortlatenzen bei kognitiven Leistungstests
No full textBesonders in den letzten Jahren erfreuen sich computerisierte Leistungsverfahren zunehmender Beliebtheit, wofür es eine Vielzahl an Gründen gibt; abgesehen von der Einfachheit, mit der diese Verfahren unter standardisierten Bedingungen vorgegeben werden können, gibt es Variablen, die durch diese Vorgabemodalitäten einfach miterfasst werden können. Diese waren Testleiter_innen zuvor nur schwer oder sehr umständlich zugänglich.
Die vorliegende Arbeit widmet sich der Bearbeitungszeit einzelner Items eines kognitiven Leistungsverfahrens und der Frage, ob ein diagnostischer Mehrwert erzielt werden kann, wenn dieser besondere Aufmerksamkeit geschenkt wird.
Um dies zu überprüfen, wurden 211 Student_innen der Universität Wien untersucht. Es wurden logistische Regressionen durchgeführt, in der Hoffnung, den Erfolg von Untersuchungsteilnehmer_innen bei einzelnen Items durch Inklusion der Zeitkomponente (zusätzlich zum Fähigkeitsparameter der Teilnehmer_in) befriedigend vorhersagen zu können.
Während gewisse Tendenzen, die im Rahmen dieser Arbeit auftraten (wie etwa jene, dass leistungsfähige Personen sich mehr Zeit für einzelne Items nehmen als weniger leistungsstarke), durchaus von Interesse für den Fachbereich der Psychologischen Diagnostik sein könnten, ergaben sich nicht die erhofften Ergebnisse – die Analyse der Bearbeitungszeit einzelner Items barg keinen diagnostischen Mehrwert hinsichtlich des Erfolgs bei der Bearbeitung.
Der Autor kommt in dieser Arbeit zu dem Schluss, dass die Interaktionen von Leistungsfähigkeit, Schwierigkeitsparameter und Bearbeitungszeit des Items nicht linearer Natur sein dürften, weshalb es komplexerer mathematischer Modelle bedarf, um diese in Bezug auf den Bearbeitungserfolg in Einklang zu bringen. Weitere Untersuchungen sind notwendig, um in dieser Hinsicht Klarheit zu schaffen.In psychological diagnostics, computerized testing, whether of personality or of aptitude, has significantly gained in popularity in recent times. There are several reasons for this, such as the simplicity with which standardized testing surroundings can be generated; also, certain variables that were previously difficult to assess or measure are now just a mouse click away for the test administrator. This thesis focuses on the response latency of single items in a test of cognitive aptitude and aims to answer the question, whether additional diagnostic value can be achieved, by paying closer attention to the time individuals spend on single items. In order to achieve this, 211 students of the University of Vienna were tested and logistic regressions were performed to ascertain whether the inclusion of a time component (in addition to a subject’s ability and the difficulty of the item) can lead to satisfactory predictions in terms of a subject’s success on single items. While certain tendencies could be observed — for example, subjects with higher ability parameters were more likely to spend more time on single items than less skilled subjects —there seemed to be no added value in the inclusion of a time component in order to predict a subjects’ success on single items. There might be several reasons for this, the author concludes that the interactions between the subjects’ ability, the difficulty of the item and time spent while working on the item are not linear in nature, which is why more complex statistical models are needed in order to clarify the relations between the aforementioned variables
Short-term SCADA-based Wind Turbine Monitoring for early failure recognition
No full textDie vorliegende Diplomarbeit, bearbeitet die Thematik rund um die Fehlerfrüherkennung von Windturbinen. Dies soll mittels Datenanalyse der vorliegenden Datensätzen aus dem SCADA-System des Unternehmens W.E.B Windenergie AG durchgeführt werden. Für eine gerechte Analyse wurden eigens für die jeweilige Problemstellung Algorithmen entworfen und infolgedessen weiter verfeinert und verallgemeinert, sodass ein möglichst flexibler Einsatz möglich sein soll. Das endgültige Ergebnis der Arbeit wurde dabei so definiert, dass sich anbahnende Fehler mittels geeigneter Vorgehensweise frühzeitig erkannt werden sollen, sodass die Reparaturplanung flexibilisiert werden kann, indem eben diese Reparaturen in Schwachwindphasen gelegt werden können. Dies ist deshalb von größer Bedeutung, da dadurch eine höhere Ausnutzung der Windkraftanlagen gewährleistet und somit auch eine umweltfreundlichere Energiebilanz und erhöhte Wirtschaftlichkeit der Windturbinen erreicht werden kann.This master thesis copes with the topic of early failure recognition for wind turbines. This has to be accomplished by a data analysis based on data acquired from a SCADA system of the company W.E.B Windenergie AG. To obtain a properly based analysis, problem-specific algorithms have been developed and further refined and generalized so that an at most flexible utilization is possible. The thesis' final objective was to detect initiating faults at an early stage so that the maintenance schedule can be made more flexible in a way that reparations can be done during phases of low wind. This is of major importance since it leads to a higher utilization of the wind turbine and thus to a more ecological energy balance and likewise to a higher profitability of the wind turbine itself
Challenges and opportunities of gravitational wave searches above 10 kHz
No full textThe first direct measurement of gravitational waves by the LIGO and Virgo collaborations has opened up new avenues to explore our Universe. This white paper outlines the challenges and gains expected in gravitational-wave searches at frequencies above the LIGO/Virgo band. The scarcity of possible astrophysical sources in most of this frequency range provides a unique opportunity to discover physics beyond the Standard Model operating both in the early and late Universe, and we highlight some of the most promising of these sources. We review several detector concepts that have been proposed to take up this challenge, and compare their expected sensitivity with the signal strength predicted in various models. This report is the summary of a series of workshops on the topic of high-frequency gravitational wave detection, held in 2019 (ICTP, Trieste, Italy), 2021 (online) and 2023 (CERN, Geneva, Switzerland)
Measuring small absorptions by exploiting photothermal self-phase modulation
No full textWe present a method for the measurement of small optical absorption coefficients. The method exploits the deformation of cavity Airy peaks that occur if the cavity contains an absorbing material with a nonzero thermorefractive coefficient dn=dT or a nonzero expansion coefficient ath. Light absorption leads to a local temperature change and to an intensity-dependent phase shift, i.e., to a photothermal self-phase modulation. The absorption coefficient is derived from a comparison of time-resolved measurements with a numerical time-domain simulation applying a Markov-chain Monte Carlo algorithm. We apply our method to the absorption coefficient of lithium niobate doped with 7 mol: % magnesium oxide and derive a value of α = (5.9 +/- 0.9) x 10^(-4)/cm. Our method should also apply to materials with much lower absorption coefficients. Based on our modeling, we estimate that, with cavity finesse values of the order of 10^4, absorption coefficients of as low as 10^(−8)/cm can be measured
Demonstration of interferometer enhancement through Einstein-Podolsky-Rosen entanglement
No full textThe recent series of gravitational-wave detections by the Advanced LIGO and Advanced Virgo observatories have launched the new field of gravitational-wave astronomy. As the sensitivity of gravitational-wave detectors is limited by the quantum noise of light, concepts from quantum metrology have been adapted to increase the observational range. Since 2010, squeezed light with reduced quantum noise has been used to achieve improved sensitivity at signal frequencies above 100 Hz. However, 100-m-long optical filter resonators would be required to also improve the sensitivity at lower frequencies, adding significant cost and complexity. Here, we report a proof-of-principle set-up of an alternative concept that achieves the broadband noise reduction by using Einstein-Podolsky-Rosen entangled states instead. We show that the desired sensitivity improvement can then be obtained with the signal recycling resonator that is already part of current observatories, providing a viable alternative to high-cost filter cavities.Einstein-Podolsky-Rosen entangled beams are sent to a 2.5-m-long cavity mimicking the signal recycling cavity of a gravitational-wave detector. By controlling the wavelength detuning, frequency-dependent squeezed vacuum states were generated.</p
Open data from the first and second observing runs of Advanced LIGO and Advanced Virgo
No full textAdvanced LIGO and Advanced Virgo are monitoring the sky and collecting gravitational-wave strain data with sufficient sensitivity to detect signals routinely. In this paper we describe the data recorded by these instruments during their first and second observing runs. The main data products are gravitational-wave strain time series sampled at 16384 Hz. The datasets that include this strain measurement can be freely accessed through the Gravitational Wave Open Science Center at http://gw-openscience.org, together with data-quality information essential for the analysis of LIGO and Virgo data, documentation, tutorials, and supporting software. (C) 2021 Published by Elsevier B.V
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