Generation and application of squeezed states of light in higher-order spatial laser modes

The next generation of gravitational-wave detectors (GWD), formed by the Einstein Telescope (ET) and Cosmic Explorer (CE), aims for improving the currently achieved sensitivities by one order of magnitude which requires significant progress in the overall noise reduction. In this regard, one discussed option for a thermal noise mitigation beyond the current ET and CE baselines is the replacement of the fundamental Gaussian TEM00 laser mode by a higher-order spatial mode. To justify this approach it is crucial to investigate whether these modes comply with the targets for all other noise sources. In this thesis, this question is investigated with respect to the quantum noise and its reduction via squeezed states of light. Cavity-enhanced second harmonic generation (SHG) is the first nonlinear process in every GWD squeezed light source. Based on the initial ET design study, the performance of the Laguerre-Gaussian LG33 mode in this process was analysed first. A numerical model for the LG33 SHG was developed and showed a good agreement with a corresponding experiment where a conversion efficiency of 45% could be achieved. However, astigmatism strongly limited the conversion efficiency as well as the output mode purity and the focus then switched to Hermite-Gaussian (HG) modes which are less sensitive in this respect. The theory on the generation of squeezed states in a type-I optical parametric amplifier was applied to higher-order HG modes, yielding that a TEM00 SHG in combination with a subsequent spatial light modulator can generate an efficient pump field in a single higher-order mode. Based on these findings, bright squeezed states at a wavelength of 1064nm in the TEM00, HG11, HG22 and HG33 mode were generated and characterised via a balanced homodyne detector in the measurement frequency range of 1MHz to 20MHz. The achieved benchmark of a quantum noise reduction of 10dB in the HG11 mode is a substantial improvement compared to previously published results. 7.5dB and 4.5dB in the HG22 and HG33 mode, respectively, were primarily limited by the available pump power. Finally, the shot-noise limited sensitivity of a tabletop Michelson interferometer with balanced homodyne detection, which is the planned readout-scheme topology for future GW detectors, was improved via the generated squeezed states in the frequency range of 1MHz to 20MHz. In this thesis, the first successful 10dB quantum noise reduction in a Michelson interferometer could be demonstrated with the TEM00 mode at 5MHz. Moreover, comparable levels of quantum noise reduction, unprecedented for any measurement application, could be achieved for the HG11 and HG22 operation at 4MHz: 8.8dB and 7.5dB, respectively. These results were mainly limited by optical loss in the squeezed light injection stage including a Faraday rotator whose aperture caused additional clipping loss for the higher-order modes. At frequencies below 4MHz, technical laser noise was the main limitation. These findings are a highly promising step in the feasibility demonstration for an improved thermal noise reduction in gravitational-wave detectors via higher-order spatial modes

Numerical analysis of LG3,3 second harmonic generation in comparison to the LG0,0 case

For coating Brownian thermal noise reduction in future gravitational wave detectors, it is proposed to use light in the helical Laguerre-Gaussian LG3,3 mode instead of the currently used LG0,0 mode. However, the simultaneous reduction of quantum noise would then require the efficient generation of squeezed vacuum states in the LG3,3 mode. Current squeezed light generation techniques employ continuous-wave second harmonic generation (SHG). Here, we simulate the SHG for both modes numerically to derive first insights into the transferability of standard squeezed light generation techniques to the LG3,3 mode. In the first part of this paper, we therefore theoretically discuss SHG in the case of a single undepleted pump mode, which, in general, excites a superposition of harmonic modes. Based on the differential equation for the harmonic field, we derive individual phase matching conditions and hence conversion efficiencies for the excited harmonic modes. In the second part, we analyse the numerical simulations of the LG0,0 and LG3,3 SHG in a single-pass, double-pass and cavity-enhanced configuration under the influence of the focusing, the different pump intensity distributions and the individual phase matching conditions. Our results predict that the LG3,3 mode requires about 14 times the pump power of the LG0,0 mode to achieve the same SHG conversion efficiency in an ideal, realistic cavity design and mainly generates the harmonic LG6,6 mode. © 2020 Optical Society of America

First results of the Laser-Interferometric Detector for Axions (LIDA)

We present the operating principle and the first observing run of a novel kind of direct detector for axions and axion-like particles in the galactic halo. Our experiment is sensitive to the polarisation rotation of linearly polarised laser light induced by an axion field, and the first detector of its kind collecting science data. We discuss our current peak sensitivity of $1.44\times 10^{-10}$ GeV$^{-1}$ (95 % confidence level) to the axion-photon coupling strength in the axion mass range of 1.97-2.01 neV which is, for instance, motivated by supersymmetric grand-unified theories. We also report on effects that arise in our high-finesse in-vacuum cavity at unprecedented optical continuous-wave intensity. Our detector already belongs to the most sensitive direct searches within its measurement band, and our first results pave the way towards surpassing the current sensitivity limits in the mass range from $10^{-8}$ eV down to $10^{-16}$ eV via quantum-enhanced laser interferometry

Design and sensitivity of a 6-axis seismometer for gravitational wave observatories

We present the design, control system, and noise analysis of a 6-axis seismometer comprising a mass suspended by a single fused silica fibre. We utilise custom-made, compact Michelson interferometers for the readout of the mass motion relative to the table and successfully overcome the sensitivity of existing commercial seismometers by over an order of magnitude in the angular degrees of freedom. We develop the sensor for gravitational-wave observatories, such as LIGO, Virgo, and KAGRA, to help them observe intermediate-mass black holes, increase their duty cycle, and improve localisation of sources. Our control system and its achieved sensitivity makes the sensor suitable for other fundamental physics experiments, such as tests of semiclassical gravity, searches for bosonic dark matter, and studies of the Casimir force

Hochschulische Bildungsangebote als Reaktion auf vermehrten Einsatz von Gesundheitstechnologien. Ein Ansatz des Projekts „HumanTec“

Malchus K, Heinze J, Kaufhold M, Klemme B, Kordisch T. Hochschulische Bildungsangebote als Reaktion auf vermehrten Einsatz von Gesundheitstechnologien. Ein Ansatz des Projekts „HumanTec“. Therapie Lernen. 2017;6(1):24-29

Einsatz von Technik im Bereich der Humandienstleistungen – Erforderliche Kompetenzen des Fachpersonals und Anforderungen an das betriebliche Bildungspersonal

Heinze J, Malchus K, Dürkopp K, Kaufhold M, Klemme B, Kordisch T. Einsatz von Technik im Bereich der Humandienstleistungen – Erforderliche Kompetenzen des Fachpersonals und Anforderungen an das betriebliche Bildungspersonal. In: VDE e.V., ed. Zukunft Lebensräume: Gesundheit, Selbstständigkeit und Komfort im demografischen Wandel. Konzepte und Technologien für die Wohnungs-, Immobilien-, Gesundheits- und Pflegewirtschaft. Berlin, Offenbach: VDE Verlag; 2016: 235-240

Qualifizierung im Kontext technologischer Entwicklungen

Malchus K, Heinze J, Kaufhold M, Klemme B, Kordisch T. Qualifizierung im Kontext technologischer Entwicklungen. In: Klemme B, Weyland U, Harms J, eds. Praktische Ausbildung in der Physiotherapie. Stuttgart: Thieme ; 2019: 138-142

Technologische Innovationen und deren Implikationen für Physiotherapeuten und Ausbilder

Klemme B, Heinze J, Dürkopp K, Kordisch T, Malchus K. Technologische Innovationen und deren Implikationen für Physiotherapeuten und Ausbilder. In: Klemme B, Weyland U, Harms J, eds. Praktische Ausbildung in der Physiotherapie. Stuttgart: Thieme ; 2019: 326-332

Open data from the first and second observing runs of Advanced LIGO and Advanced Virgo

Advanced 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