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20th Lomonosov Conference on Elementary Particle Physics, Lomonosov, Moscow, Russia, 19 Aug 2021 - 25 Aug 2021; Moscow University physics bulletin 77(2), 120 - 125 (2022). doi:10.3103/S002713492202045X, The Any Light Particle Search (ALPS II) is a light shining through a wall (LSW) experiment searching for axion-like elementary particles in the sub-eV mass range, which are motivated by astrophysics and cosmology and fulfill the requirements for being dark matter. ALPS II aims to measure an axion-to-photon coupling of $2\times 10^{-11}\textrm{ GeV}^{-1}$, which is several orders of magnitude better than that of previous LSW experiments and will thus investigate a new parameter range. The increased performance is achieved by enhancing the magnetic field interaction length to $2\times 10^{6}$ m and by amplifying the signal in an optical cavity on each side of a light-tight barrier. The expected signal is in the order of 1 photon per day, which will be measured by photon detectors with very low dark count rates of $\mathcal{O}(10^{-6}\textrm{ Hz})$. This article gives a technical overview on the experiment design, previous and ongoing investigations, and the current status with focus on the single photon detection., Published by Faraday Press, New York, NY

19th International Workshop on Low Temperature Detectors, LTD-19, Hamburg, USA, 19 Jul 2021 - 29 Jul 2021; Journal of low temperature physics 209(3-4), 355 - 362 (2021). doi:10.1007/s10909-022-02720-0, Transition Edge Sensors (TESs) have found widespread application in fundamental studies due to their low background rate, high efficiency, and excellent energy resolution. This makes them suitable candidates for ALPS II, which investigates the existence of new particles (axions and axion-like-particles) which couple very weakly to photons. ALPS II anticipates an extremely low signal rate < 10$^{−5}$ cps (amounting to ∼1–2 photons a day). The detection of these low energy (∼1 eV, 1064 nm) photons with a high energy resolution is necessary for ALPS II. We show that with our TES setup, we can analyze the TES pulses with different methods such as pulse fitting and Principal Component Analysis (PCA). These achieve (using the standard deviation) an energy resolution $(ΔE/E)$ down to ∼8%. The pulse analysis, with a chosen fitting approach, assists also in achieving a very low dark count rate $O(10^{−6})$ cps for 1064 nm photon signal searches in the TES., Published by Springer Science + Business Media B.V., Dordrecht

We propose to combine differential wave-front sensing (DWS) and differential power sensing (DPS) in a Mach-Zehnder type interferometer for measuring the rotational dynamics of a test-mass. Using the DWS method, a high sensitive measurement of 6 nrad Hz−1/2 in sub-Hz frequencies can be provided around the test-mass nominal position (±0.11 mrad), whereas the measurement of a wide rotation range (±5 mrad) is realized by the DPS method. The interferometer can be combined with deep frequency modulation (DFM) interferometry for measurement of the test-mass translational dynamics. The setup and the resulting interferometric signals are verified by simulations. An optimization algorithm is applied to find suitable positions of the lenses and the waist size of the input laser in order to determine the best trade of between the slope of DWS, dynamic range of DPS, and the interferometric contrast. Our simulation further allows to investigate the layout for robustness and design tolerances. We compare our device with a recent experimental realization of a DFM interferometer and find that a practical implementation of the interferometer proposed here has the potential to provide translational and rotational test-mass tracking with state-of-the-art sensitivity. The simple and compact design, and especially the capability of sensing the test-mass rotation in a wide range and simultaneously providing a high-precision measurement close to the test-mass nominal position makes the design especially suitable for example for employment in torsion pendulum setups., Sensors, 21 (1), ISSN:1424-8220

The development and investigation of laser interferometry concepts for performing precise length measurements at frequencies below 1Hz is the main topic of this thesis. These concepts are quintessential for space-based measurements of gravitational waves or the Earth gravity field. For the Laser Interferometer Space Antenna (LISA) and future satellite geodesy missions, various interferometer types have been studied between 2014 and 2018 at the Albert Einstein Institute (AEI) in Hannover as a part of the work presented here. The first part of this thesis presents conceptual design studies of phase reference distribution systems (PRDSs) for LISA. The usage of Telescope Pointing is the baseline mechanism for the current LISA design and implies the need for a light-exchanging backlink connection between two rotating optical benches within one satellite. Different backlink implementations are presented and analyzed, the final choice however remains one of the last open questions for the LISA optical metrology. A test-bed for comparing three backlinks with each other in a single, so-called Three-Backlink interferometer (TBI) experiment, has been simulated and a detailed noise estimation, including a critical stray light analysis, is presented. A free-beam connection between two moving set-ups was established by which the full functionality of the experimental environment was validated. The design of the TBI has been completed and the experiment, consisting of two rotating quasi-monolithic optical benches, is currently under construction. The full experiment will enable to test the performance of LISA backlink candidates with a precision of 1 pm/√Hz in a relevant environment. The second part of this thesis describes alternative interferometer techniques for reducing the complexity of optical set-ups, while modern digital signal processing is applied for recovering the desired phase information. The simplifications in the optical part enables multi-channel operation and multi-degree of freedom readout, which is required for future gradiometers in satellites consisting of six or more test masses. An experiment simulating such a test mass readout with only a single optical component has been established. Interferometric readout noise levels of 1.0pm/√Hz at 100mHz were achieved by using deep frequency modulation interferometry (DFMI), a novel technique developed as part of this thesis., Die Entwicklung von Laserinterferometern für präzise Längenänderungsmessungen im 1mHz-Frequenzbereich ist das Kernthema dieser Arbeit. Diese finden Anwendung in der Detektion von Gravitationswellen und der Messung des Erdschwerefeldes aus dem Weltraum. Verschiedene Interferometerkonzepte wurden für die Laser Interferometer Space Antenna (LISA)- und zukünftige geodätische Missionen innerhalb der hier dargestellten Arbeit am Albert-Einstein-Institut (AEI) in Hannover zwischen 2014 und 2018 untersucht. Der erste Teil dieser Arbeit befasst sich mit einer Designstudie über unterschiedliche Phasenreferenzverteilungssysteme (PRDSs) für LISA. Das derzeitige Design sieht das sogenannte Telescope Pointing als Basis-Mechanismus vor, wodurch eine Backlink-Verbindung zwischen zwei rotierenden optischen Bänken innerhalb eines Satelliten benötigt wird. Die Laser werden hiermit zwischen den beiden Interferometern ausgetauscht. Eine konkrete Realisierung dieses Backlinks ist eine der letzten offenen Fragen für das optische Design von LISA. Das sogenannte Drei-Backlink Interferometer (TBI) wurde speziell entworfen und dient als Testumgebung, in welcher drei Backlinks in einem einzelnen Aufbau miteinander verglichen werden. Optische Simulationen und eine Vorhersage möglicher Rauschquellen werden in dieser Arbeit präsentiert. Eine Freistrahl-Verbindung zwischen zwei rotierenden Bänken wurde bereits untersucht und es konnte gezeigt werden, dass die experimentelle Infrastruktur voll funktionsfähig ist. Das Design des Drei-Backlink Experiments ist abgeschlossen und es wird derzeit konstruiert. Der zweite Teil dieser Arbeit beschreibt alternative Interferometertechniken um die Komplexität optischer Aufbauten zu reduzieren. Moderne digitale Verarbeitungssysteme werden benutzt, um die gewünschte Phaseninformation zurückzugewinnen. Eine Vereinfachung der Optik ermöglicht den Betrieb mehrerer Kanäle gleichzeitig und die Auslesung vieler Freiheitsgrade. Diese Techniken werden in zukünftigen Satelliten-Gradiometern benötigt, um die Bewegung mehrerer Testmassen zu bestimmen. Dies wurde in einem optischen Aufbau mit nur einer einzelnen optischen Komponente simuliert. Mit tiefen Laserfrequenzmodulationen (DFMI), einer im Rahmen dieser Arbeit entwickelten Methode, konnte eine Messgenauigkeit von unter 1.0 pm/√Hz bei 100mHz erreicht werden.

GRACE Follow-On ist eine gravi - metrische Weltraummission, mit der anhand eines Satellitenpaares das Erdschwerefeld vermessen wird. Die monatlichen Karten des Erdschwerefelds, die aus den Daten von GRACE konstruiert werden, haben sich als wichtiges Werkzeug für Klima- und Geowissenschaftler etabliert. Ein Forschungsteam vom Institut für Gravitationsphysik stellt die Entwicklung neuer Sensoren für die Satellitengravimetrie vor.