arXiv subjects

Oliver Gerberding

Publications and source records attributed to Oliver Gerberding.

At least 19 recordsLinked to original sources

arXiv2026

Demonstration of a compact optical resonator-based displacement sensing technique with sub-femtometer precision

We demonstrate sub-femtometer displacement-sensing results achieved with a compact optical resonator-based laser interferometry technique called heterodyne cavity-tracking, intended for local displacement or inertial sensing with ultra-high sensitivity. Displacement sensing at this sensitivity is required for ambitious improvements to current gravitational-wave detectors and to enable future ground- and space-based observatories. The optical topology employs a centimeter-scale dynamic cavity incorporating a proof mass, and the relative length fluctuations of this cavity are measured using a heterodyne readout. The fundamental limits of the technique lie significantly below the femtometer level and are ultimately defined by the coating thermal noise of the cavity mirrors. In our experimental demonstration, we achieve a sub-femtometer per Hz$^{1/2}$ displacement sensitivity for Fourier frequencies above 8 Hz and a sub-picometer per Hz$^{1/2}$ sensitivity above 3 mHz, with the sensitivity at lower frequencies limited by mechanical and temperature-induced noise sources. When the length of the dynamic cavity was intentionally actuated, the technique could track a maximum motion of about 0.6 $\mu$m, thereby achieving a dynamic range of roughly ten orders of magnitude in displacement sensing. We thus demonstrate the key features of this scheme - sub-femtometer performance and a dynamic range spanning ten orders of magnitude - in a laboratory setting, paving the way for development of an integrated system. Such a system is a currently unrealized technology that is necessary for precision physics experiments in the coming decades.

physics.ins-det↗

arXiv2025

Demonstrating sub-picometer non-reciprocity levels in the Three-Backlink Experiment for LISA

The current planned space-based gravitational-wave detectors require a bidirectional optical connection, referred to as Backlink, between two adjacent optical benches to provide a mutual phase reference for the local interferometric measurements. However, if the Backlink shows asymmetry between the two propagation directions, the effective optical pathlengths of the counter-propagating beams can introduce a differential phase noise, called non-reciprocity, into the main interferometric measurement that will limit the achievable accuracy in time-delay interferometry (TDI) post-processing. Hence, it is important to understand the properties of the Backlink to ensure that it will not compromise the interferometric detection. The Three-Backlink Experiment (3BL), which consists of an optical test facility with two rotatable benches, was designed under the Laser Interferometer Space Antenna (LISA) framework to study the performance of three Backlink configurations: two fiber-based and one free-beam scheme. In this paper, we report recent experimental results from the 3BL. We describe the commissioning and the subsequent noise mitigation. We achieve a setup noise floor below $1\text{ pm}\sqrt{\text{Hz}}$ across most of the LISA measurement band, and provide an understanding of the current technical limitations. With this low-noise baseline, we measured the performance of the three Backlink implementations under non-rotational conditions. We show that all three Backlinks reach sub-picometer non-reciprocity levels across most of the frequency band, with the remaining part dominated by the mentioned testbed noise. This enabled us to conduct a preliminary study of the Backlink inherent noise, where we emphasized on the backscatter noise intrinsic to a straightforward fiber-based Backlink, as this is the current baseline for LISA.

physics.optics↗

arXiv2025

Construction techniques and commissioning of the Three-Backlink Experiment for the LISA mission

Designed to detect gravitational waves in the lower-frequency band, the space mission LISA will open a new window to astronomy after its launch in the 2030s. Each LISA spacecraft houses two optical benches that require the exchange of a phase reference between them via an optical connection, called a Backlink. Here we present the construction and commissioning of an ultra-stable quasi-monolithic optical testbed to investigate different Backlink implementations: a direct fiber, a frequency-separated fiber, and a free-beam link, compared in the Three-Backlink Experiment. Dedicated alignment techniques crucial for the construction of these optical benches are presented together with the development of a high-precision beam alignment and measurement tool - a Calibrated Quadrant Photodiode Singleton. An upper limit for the performance of all three investigated Backlink schemes, as determined by initial experiments, can be set at a $15\text{pm}/\sqrt{\text{Hz}}$-equivalent level within the LISA band, spanning 0.1mHz to 1Hz. Our measurements were able to verify the successful construction and commissioning of this very complex interferometer as an interferometric laboratory testbed for LISA. We find no limitations due to the construction on the here reported performance levels. Our results can support the construction of high-precision metrology testbeds for space-based laser interferometry for future gravitational wave or geodesy missions.

physics.optics↗

arXiv2025

Distributed Acoustic Fiber Sensing for Research Campuses and Large Scientific Infrastructures -- The Hamburg WAVE proto-network

Here, we demonstrate and investigate how Distributed Acoustic Sensing (DAS) can be utilized on research campuses and in large scientific infrastructures to study environmental vibrations and reduce their impact on high-precision experiments. We first discuss the potential of DAS in the context of particle accelerators, gravitational wave detection experiments and research campuses. Next, we present the results of our seismic measurement campaign conducted with our proto-network, which involved the probing of over 12 km of fiber, in May 2021. This campaign was conducted by the Hamburg WAVE initiative in Science City Hamburg Bahrenfeld and included DESY, the European XFEL, PETRA III and the University of Hamburg. Our proto-network confirms the ability to observe natural, anthropogenic, and infrastructural vibrations and how and where these couple into different parts of the heterogeneously set up fiber network. We also present results on a study of noise and motion coupling aspects of DAS probing double-redundant fiber loops in a unique environment, the European XFEL. Our results show that DAS greatly benefits research campuses and large scientific infrastructures and they highlight the opportunities and challenges of implementing and operating such seismic networks.

physics.ins-det↗

arXiv2025

GEMINI: The First Underground Testbed for Seismic Isolation and Interplatform Control in Next-Generation Gravitational-Wave Detectors

GEMINI is an underground research and development facility dedicated to advancing seismic isolation and control technologies for future gravitational-wave observatories, including the Einstein Telescope (ET) and the Lunar Gravitational-Wave Antenna (LGWA). This paper presents the technical design and theoretical framework of GEMINI's active seismic isolation platforms, including detailed noise budget analyses, performance predictions, and residual platform motion evaluations. The GEMINI platforms are designed to achieve unprecedented vibration isolation, targeting motion suppression across the 10 mHz to 10 Hz frequency band, and with the goal to make them the quietest platforms of their kind. In the context of ET, GEMINI will enable the development and validation of inter-platform control strategies essential for the stabilization of auxiliary degrees of freedom of its interferometers. GEMINI will also support the testing of cryogenic payloads and ultra-sensitive inertial sensors required for LGWA. By integrating advanced cryogenic systems, precision inertial sensors, and state-of-the-art vibration isolation technologies, GEMINI will serve as a versatile testbed for next-generation ground-based gravitational-wave detectors and lunar seismometry missions.

physics.ins-det↗

arXiv2025

Using tunable coherence for reaching micrometer coherence lengths and suppressing stray light in a power-recycled Michelson interferometer

By reentering into laser interferometers, scattered or stray light introduces non-linear noise. This is a major limitation of precision interferometers as preventing such parasitic light is nearly impossible. Thus, substantial effort is put into mitigating the reentering of these fields in various ways. Ground-based laser interferometric gravitational wave detectors employ such mitigation techniques to reduce otherwise restrictive stray light noise. However, they are now reaching sensitivities where conventional mitigation techniques reach limitations. Further improvements planed for future observatories are placing even more demanding constraints on tolerable stray light power. We previously presented tunable coherence as a possible technique to ease these constraints and suppress unwanted coherent interference. For these promising demonstrations, the remaining coherence length and achievable suppression in length-constrained layouts was limited, among other things, by the used pseudo-random-noise phase modulation frequency. In this work, we demonstrate stray light suppression and cavity performance at modulation frequencies up to 10 GHz. This reduces the remaining coherence to a few centimeter in an interferometer, and even to the scale of the laser wavelength in a cavity. We further present a first demonstration of tunable coherence in a power-recycled Michelson interferometer, successfully suppressing stray light in a more complex topology.

physics.optics↗

arXiv2025

Reducing suspension control noise with interferometric sensors -- an experimental concept

One of the limiting noise sources of ground-based gravitational wave detectors at frequencies below 30 Hz is control-induced displacement noise. Compact laser interferometric sensors are a prime candidate for improved local displacement sensing. In this paper we present the design of an experiment that aims to demonstrate the advantages of interferometric sensors over shadow sensors. We focus on the compact balanced readout interferometer (COBRI) - a sensor currently in development that is based on deep frequency modulation. We mount COBRIs on two HAM Relay Triple Suspension (HRTS) systems that suspend two mirrors forming an optical cavity. By measuring the length stability of this cavity relative to a stable reference we aim to probe the direct motion reduction when using COBRIs for active damping and we aim to investigate their behavior and auxiliary functions, such as absolute ranging, in the context of the 6 degree-of-freedom controls of the suspensions. Here we describe the design of the experiment and simulations of the achievable noise levels that were obtained using mechanical models of the HRTS suspensions. We discuss all relevant noise sources, the modeled influence of the interferometric sensor damping and the current limitations and necessary improvements of our testing facility in terms of seismic pre-isolation to achieve a shadow sensor limited noise at around 5 Hz, where, according to our simulations, we can demonstrate superior performance for COBRIs in the longitudinal degree of freedom.

physics.ins-det↗

arXiv2025

Scattered light reduction in Sagnac Speed Meters with Tunable Coherence

Sagnac Speed Meter and ring resonators can be used as high precision instruments, but they are limited in their sensitivity through scattered light causing non-linear noise. Here, we experimentally demonstrate a technique called Tunable Coherence, where the long coherence length of the laser is broken in a controlled way, to suppress the coupling of scattered light in a Sagnac interferometer. We demonstrate a scattered light suppression of 24.2 dB in a Sagnac interferometer and discuss the experimental limitations. Further, we show an analytical discussion on how Tunable Coherence could be a fundamental solution to light scattering back from optical surfaces into the counter propagating beam, which is an issue particularly in ring resonators.

physics.optics↗

arXiv2025

Adjustable picometer-stable interferometers for testing space-based gravitational wave detectors

Space-based gravitational wave detectors, such as the Laser Interferometer Space Antenna (LISA), use picometer-precision laser interferometry to detect gravitational waves at frequencies from 1 Hz down to below 0.1 mHz. Laser interferometers used for on-ground prototyping and testing of such instruments are typically constructed by permanently bonding or gluing optics onto an ultra-stable bench made of low-expansion glass ceramic. This design minimizes temperature coupling to length and tilt, which dominates the noise at low frequencies due to finite temperature stability achievable in laboratories and vacuum environments. Here, we present the study of an alternative opto-mechanical concept where optical components are placed with adjustable and freely positionable mounts on an ultra-stable bench, while maintaining picometer length stability. With this concept, a given interferometer configuration can be realised very quickly due to a simplified and speed-up assembly process, reducing the realisation time from weeks or months to a matter of hours. We built a corresponding test facility and verified the length stability of our concept by measuring the length change in an optical cavity that was probed with two different locking schemes, heterodyne laser frequency stabilisation and Pound-Drever-Hall locking. We studied the limitations of both locking schemes and verified that the cavity length noise is below 1 pm/sqrt(Hz) for frequencies down to 3 mHz. We thereby demonstrate that our concept can simplify the testing of interferometer configurations and opto-mechanical components and is suitable to realise flexible optical ground support equipment for space missions that use laser interferometry, such as future space-based gravitational wave detectors and satellite geodesy missions.

physics.ins-det↗

arXiv2025

Tunable coherence laser interferometry: demonstrating 40dB of straylight suppression and compatibility with resonant optical cavities

A major limitation of laser interferometers using continuous wave lasers are parasitic light fields, such as ghost beams, scattered or stray light, which can cause non-linear noise. This is especially relevant for laser interferometric ground-based gravitational wave detectors. Increasing their sensitivity, particularly at frequencies below 10 Hz, is threatened by the influence of parasitic photons. These can up-convert low-frequency disturbances into phase and amplitude noise inside the relevant measurement band. By artificially tuning the coherence of the lasers, using pseudo-random-noise (PRN) phase modulations, this influence of parasitic fields can be suppressed. As it relies on these fields traveling different paths, it does not sacrifice the coherence for the intentional interference. We demonstrate the feasibility of this technique experimentally, achieving noise suppression levels of 40 dB in a Michelson interferometer with an artificial coherence length below 30 cm. We probe how the suppression depends on the delay mismatch and length of the PRN sequence. We also prove that optical resonators can be operated in the presence of PRN modulation by measuring the behavior of a linear cavity with and without such a modulation. By matching the resonators round-trip length and the PRN sequence repetition length, the classic response is recovered.

physics.optics↗

arXiv2024

Characterizing seismic isolation using convolutional neural networks and Wiener filters

We investigate seismic motion propagation through a passively isolated mechanical system, using Wiener filters and convolutional neural networks with time-dilation layers. The goal of this study was to explore the capabilities of neural networks and Wiener filters in characterizing a mechanical system from the measurements. The mechanical system used is a testbed facility for technology development for current and future gravitational wave detectors, "VATIGrav", currently being commissioned at University of Hamburg. It consists of a large vacuum chamber mounted on four active vibration isolators with an optical table inside, mounted on four passive vibration isolators. In this paper we have used seismic data recorded on the ground and on the optical table inside the chamber. The data were divided in 6 hours for training and another 6 hours for validation, focusing on inferring 150-second stretches of time series of table motion from the ground motion in the frequency range from $0.1~\mathrm{Hz}$ to about $50~\mathrm{Hz}$. We compare the performance of a neural network with FTT-based loss function and with Huber loss function to single-input, single-output (SISO) and multiple-input, single-output (MISO) Wiener filters. To be able to compute very large MISO Wiener filters (with 15,000 taps) we have optimized the calculations exploiting block-Toeplitz structure of the matrix in Wiener-Hopf equations. We find that for the given task SISO Wiener filters outperform MISO Wiener filters, mostly due to low coherence between different motion axes. Neural network trained with Huber loss performs slightly worse than Wiener filters. Neural network with FFT-based loss outperforms Wiener filters in some frequency regions, particularly with low amplitudes and reduced coherence, while it tends to slightly underestimate the peaks, where Wiener filters perform better.

physics.ins-det↗

arXiv2024

Dual balanced readout for scattered light noise mitigation in Michelson interferometers

Ground-based gravitational wave detectors use laser interferometry to detect the minuscule distance change between test masses caused by gravitational waves. Stray light that scatters back into the interferometer causes transient signals that can cover the same frequency range as a potential gravitational wave signal. Scattered light noise is a potentially limiting factor in current and future detectors thus making it relevant to find new ways to mitigate it. Here, we demonstrate experimentally a technique for the subtraction of scattered light noise from the displacement readout of a Michelson interferometer. It is based on using a balanced homodyne detector at both the symmetric and the antisymmetric port. While we have been able to demonstrate a noise reduction of \SI{13.2}{\decibel}, the readout scheme seems to be only limited by the associated noise couplings, with no theoretical limit to the scattered light suppression itself other than shot noise. We also discuss challenges for using the dual balanced homodyne detection scheme in more complex interferometer topologies, which could lead to improvements in scattered light noise mitigation of gravitational wave detectors.

physics.ins-det↗

arXiv2024

Integrating high-precision and fringe-scale displacement sensing using heterodyne cavity-tracking

We present a heterodyne stabilized cavity-based interferometer scheme that can serve as a compact and high-sensitivity displacement sensor with a fringe-scale operating range. The technique, in principle, can reach a sub-femtometer noise floor and an operating range on the order of one laser wavelength at $\lambda \approx 1\,\mu m$. With our current experimental setup, we achieve a sensitivity of about $260 fm/\sqrt{\mathrm{Hz}}$ at $1\,Hz$ and $46 fm/\sqrt{\mathrm{Hz}}$ at around $130\,Hz$. By probing a length actuated cavity, we demonstrate six orders of magnitude of dynamic range for displacement measurement, reaching a maximum motion of $0.15\,\mu m$. The tracking bandwidth and displacement range are limited by analog effects in the signal digitization and are extendable in the future.

physics.optics↗

arXiv2024

The Lunar Gravitational-wave Antenna: Mission Studies and Science Case

The Lunar Gravitational-wave Antenna (LGWA) is a proposed array of next-generation inertial sensors to monitor the response of the Moon to gravitational waves (GWs). Given the size of the Moon and the expected noise produced by the lunar seismic background, the LGWA would be able to observe GWs from about 1 mHz to 1 Hz. This would make the LGWA the missing link between space-borne detectors like LISA with peak sensitivities around a few millihertz and proposed future terrestrial detectors like Einstein Telescope or Cosmic Explorer. In this article, we provide a first comprehensive analysis of the LGWA science case including its multi-messenger aspects and lunar science with LGWA data. We also describe the scientific analyses of the Moon required to plan the LGWA mission.

gr-qc↗

arXiv2024

High Precision Inertial Sensors on a One Inch Diameter Optic

Compact, high-precision inertial sensors are needed to isolate many modern physics experiments from disturbances caused by seismic motion. We present a novel inertial sensor whose mechanical oscillator fits on a standard one-inch diameter optic. The oscillators achieve a Quality factor of over 600,000 and a resonance frequency of 50\,Hz, giving them a suspension thermal noise floor lower than all commercially available inertial sensors. The oscillator is combined with a Pound-Drever-Hall based readout scheme that achieves a displacement noise of 100\,f\msqrthz above 0.2\,Hz. We integrate the oscillator and readout to make two inertial sensors. Of order n$g$ performance is achieved in a broad band from 0.1\,Hz to 200\,Hz. Below 20\,Hz, the sensor presented here offers comparable performance to the best inertial sensors available today while being a fraction of the size. Above 20\,Hz, the sensor is, to the author's knowledge, the best demonstrated in the literature to date for a device of this style, with a self-noise floor of 0.1\,n$g$\sqrthz. The excellent performance of the sensors across the relevant seismic frequencies, vacuum compatibility, and compact size make it a prime candidate for integration into sophisticated seismic isolation schemes, such as those used by gravitational wave detectors.

physics.ins-det↗

arXiv2024

On the Development of an RFSoC-Based Ultra-Fast Phasemeter With GHz Bandwidth

Precise measurements of the frequency and phase of an electrical or optical signal play a key role in various branches of science and engineering. Tracking changing laser frequencies is especially demanding when the lasers themselves are noisy or if the frequencies rapidly change because they encode highly dynamic signals in, e.g., Doppler-ranging or dynamic cavity readout. Here, to address these and other possible applications, we report the development of a high signal bandwidth (> 2 GHz) and high tracking bandwidth (2 MHz) multi-channel Phasemeter. The implementation utilizes an all-digital phase-locked loop realized within the field programmable gate array (FPGA) part of a radio frequency system-on-chip (RFSoC), the programmable logic (PL). The new features of the phasemeter are obtained by operating the PL at its timing limits and introducing a multi-demodulation and phase accumulation scheme. We present performance measurements, discuss the role of the high tracking bandwidth for tracking highly dynamic signals, and demonstrate ultra-stable phase locking of a beat note between two widely tunable external cavity diode lasers. We achieve a phase-noise floor in the sub-milli radian regime when comparing two signals, even for GHz frequencies, and demonstrate stable tracking of signals with a frequency change rate of 240 GHz/s.

physics.ins-det↗

arXiv2023

Designing Gram-Scale Resonators for Precision Inertial Sensors

Recent advances in glass fabrication technology have allowed for the development of high-precision inertial sensors in devices weighing in the order of grams. Gram-scale inertial sensors can be used in many applications with tight space or weight requirements. A key element of these devices' performance is the behaviour of a mechanical resonator. We present a detailed study on the design of resonators for such sensors. First, we consider how the mechanical parameters of a resonator couple with an inertial sensor's performance. Then, we look at how to geometrically design resonators to achieve specific mechanical behaviour without undergoing brittle failure. Both analytic tools and finite element analysis are used to this end. We then derive expressions that can be used to optimise the performance of an inertial sensor for a specific sensitive bandwidth. A simple geometry used throughout the field is studied as an example. However, the results are presented in a general form so they can easily be adapted to any required geometry and use case. Ultimately, the results presented here guide the design of gram-scale inertial sensors and will improve the performance of devices that follow them.

physics.ins-det↗

arXiv2023

The payload of the Lunar Gravitational-wave Antenna

The toolbox to study the Universe grew on 14 September 2015 when the LIGO-Virgo collaboration heard a signal from two colliding black holes between 30-250 Hz. Since then, many more gravitational waves have been detected as detectors increased sensitivity. However, the current detector design sensitivity curves still have a lower cut-off of 10 Hz. To detect even lower-frequency gravitational-wave signals, the Lunar Gravitational-wave Antenna will use an array of seismic stations in a permanently shadowed crater. It aims to detect the differential between the elastic response of the Moon and the suspended inertial sensor proof mass motion induced by gravitational waves. A cryogenic superconducting inertial sensor is under development that aims for fm/rtHz sensitivity or better down to 1 Hz and is planned to be deployed in seismic stations. Here, we describe the current state of research towards the inertial sensor, its applications and additional auxiliary technologies in the payload of the lunar gravitational-wave detection mission.

gr-qc↗