@article{c7b00b8005af451ba3fba792ab4b5dd4,
title = "Tunable Coherence Laser Interferometry: Demonstrating 40 dB of Stray Light Suppression and Compatibility with Resonant Optical Cavities",
abstract = "A major limitation of laser interferometers using continuous wave lasers are parasitic light fields, such as ghost beams, scattered or stray light, that can cause nonlinear 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. ",
keywords = "Atomic, Molecular, and Optical Physics, Optics, Instrumentation and Methods for Astrophysics, General Relativity and Quantum Cosmology, Instrumentation and Detectors",
author = "Daniel Voigt and Leonie Eggers and Katharina-Sophie Isleif and Koehlenbeck, \{Sina M.\} and Melanie Ast and Oliver Gerberding",
year = "2025",
month = may,
day = "28",
doi = "10.1103/PhysRevLett.134.213802",
language = "English",
volume = "134",
journal = "Physical Review Letters",
issn = "0031-9007",
publisher = "American Physical Society",
number = "21",
}
@article{e094431d12174391a11d0cf271d80b75,
title = "Seismic Noise Contributions to EuXFEL Bunch Arrival Time Jitter from Ocean-Generated Microseism",
abstract = "Measurements of the bunch arrival times at the European XFEL show noise contributions in the spectral range between 0.05 Hz and 0.5 Hz with peak-to-peak jitter of up to 25 fs. Correlation with Distributed Acoustic Sensing (DAS) measurements confirms the seismic origin. The seismic noise in this frequency band is known to be ocean-generated microseism. Both primary and secondary ocean-generated microseism were identified using seismometers and a numerical ocean wave model. Whereas secondary microseism has a strong impact on the bunch arrival time, primary microseism has no notable effect. Rayleigh waves cause the effect, while Love waves have minimal impact. In the presented cases, the noise originates from the North Atlantic and/or the North Sea. The amplitude of the noise depends on the local weather conditions and is much stronger in winter. Ocean-generated microseism is a significant bottleneck that must be addressed to achieve femtosecond bunch arrival time stability in the sub-Hz regime.",
keywords = "Distributed Acoustic Sensing, European XFEL, large-scale FEL, microseism, stability",
author = "Erik Genthe and Czwalinna, \{Marie Kristin\} and Bj{\"o}rn Lautenschlager and Holger Schlarb and Celine Hadziioannou and Oliver Gerberding and Katharina-Sophie Isleif",
year = "2025",
month = apr,
day = "25",
doi = "10.1017/hpl.2025.40",
language = "English",
journal = "High Power Laser Science and Engineering",
issn = "2052-3289",
publisher = "Cambridge University Press",
}
@techreport{881e072d994e47d7a0f1a320d50c5d3e,
title = "Scattered light reduction in Sagnac Speed Meters with Tunable Coherence",
abstract = "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. ",
keywords = "Physics - Optics, Astrophysics - Instrumentation and Methods for Astrophysics, General Relativity and Quantum Cosmology, Physics - Instrumentation and Detectors",
author = "Leonie Eggers and Daniel Voigt and Oliver Gerberding",
year = "2025",
month = feb,
day = "11",
language = "English",
series = "arXiv e-prints",
type = "WorkingPaper",
}
@techreport{e9bffe7b56144b988add55d1ea6ee639,
title = "Adjustable picometer-stable interferometers for testing space-based gravitational wave detectors",
abstract = " 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. ",
keywords = "physics.ins-det, gr-qc",
author = "Marcel Beck and Subrahmanya, \{Shreevathsa Chalathadka\} and Oliver Gerberding",
year = "2025",
month = feb,
day = "3",
language = "English",
type = "WorkingPaper",
}
@article{947b8f54c37444d3b0a4583f5881d333,
title = "Integrating high-precision and fringe-scale displacement sensing using heterodyne cavity-tracking",
abstract = "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 λ ≈ 1 μm. With our current experimental setup, we achieve a sensitivity of about 260 Hz at 1 Hz and 46 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 μm. The tracking bandwidth and displacement range are limited by analog effects in the signal digitization and are extendable in the future.",
author = "\{Chalathadka Subrahmanya\}, Shreevathsa and Darsow-Fromm, \{Christian Domenic\} and Oliver Gerberding",
year = "2025",
month = jan,
day = "28",
doi = "10.1364/OE.540189",
language = "English",
volume = "33",
pages = "4044--4054",
journal = "Optics express",
issn = "1094-4087",
publisher = "The Optical Society",
number = "3",
}
@article{2db530ffc8104b7584794b354ab3813b,
title = "The Lunar Gravitational-wave Antenna: Mission Studies and Science Case",
abstract = "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. ",
keywords = "General Relativity and Quantum Cosmology, Astrophysics - Cosmology and Nongalactic Astrophysics",
author = "Parameswaran Ajith and \{Amaro Seoane\}, Pau and \{Arca Sedda\}, Manuel and Riccardo Arcodia and Francesca Badaracco and Enis Belgacem and Stefano Benetti and Alexey Bobrick and Alessandro Bonforte and Elisa Bortolas and Valentina Braito and Marica Branchesi and Adam Burrows and Enrico Cappellaro and \{Della Ceca\}, Roberto and Chandrachur Chakraborty and \{Chalathadka Subrahmanya\}, Shreevathsa and Coughlin, \{Michael W.\} and Stefano Covino and Andrea Derdzinski and Aayushi Doshi and Maurizio Falanga and Stefano Foffa and Alessia Franchini and Alessandro Frigeri and Yoshifumi Futaana and Oliver Gerberding and Kiranjyot Gill and \{Di Giovanni\}, Matteo and Giudice, \{Ines Francesca\} and Margherita Giustini and Philipp Gl{\"a}ser and Jan Harms and \{van Heijningen\}, Joris and Francesco Iacovelli and Kavanagh, \{Bradley J.\} and Taichi Kawamura and Arun Kenath and Elisabeth-Adelheid Keppler and Chiaki Kobayashi and Goro Komatsu and Valeriya Korol and N.\textasciitilde{}V. Krishnendu and Prayush Kumar and Francesco Longo and Michele Maggiore and Michele Mancarella and Andrea Maselli and Alessandra Mastrobuono-Battisti and Francesco Mazzarini and Andrea Melandri and Daniele Melini and Sabrina Menina and Giovanni Miniutti and Deeshani Mitra and Javier Mor{\'a}n-Fraile and Suvodip Mukherjee and Niccol{\`o} Muttoni and Marco Olivieri and Francesca Onori and \{Alessandra Papa\}, Maria and Ferdinando Patat and Tsvi Piran and Silvia Piranomonte and \{Roper Pol\}, Alberto and Pookkillath, \{Masroor C.\} and R. Prasad and Vaishak Prasad and \{De Rosa\}, Alessandra and Chowdhury, \{Sourav Roy\} and Roberto Serafinelli and Alberto Sesana and Paola Severgnini and Angela Stallone and Jacopo Tissino and Hrvoje Tkal{\v c}i{\'c} and Lina Tomasella and Martina Toscani and David Vartanyan and Cristian Vignali and Lucia Zaccarelli and Morgane Zeoli and Luciano Zuccarello",
year = "2025",
month = jan,
day = "28",
doi = "10.1088/1475-7516/2025/01/108",
language = "English",
volume = "2025",
journal = "Journal of cosmology and astroparticle physics ",
issn = "1475-7516",
publisher = "IOP",
number = "1",
}
@techreport{138271a91a4a4ee7b6dcb0cad4d8a61e,
title = "Tunable coherence laser interferometry: demonstrating 40dB of straylight suppression and compatibility with resonant optical cavities",
abstract = "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. ",
keywords = "Physics - Optics, Astrophysics - Instrumentation and Methods for Astrophysics, General Relativity and Quantum Cosmology, Physics - Instrumentation and Detectors",
author = "Daniel Voigt and Leonie Eggers and Katharina-Sofie Isleif and Koehlenbeck, \{Sina M.\} and Melanie Ast and Oliver Gerberding",
year = "2025",
month = jan,
day = "20",
language = "English",
series = "arXiv e-prints",
type = "WorkingPaper",
}
@article{264274a0143948d2bf318589d9ac05df,
title = "On the development of an RFSoC-based ultra-fast Phasemeter with GHz bandwidth",
abstract = "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 specifically 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, 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. 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, even for GHz signals, and demonstrate stable tracking of signals with a frequency change rate of 240 GHz/s. ",
keywords = "Field programmable gate arrays, Frequency measurement, Phase locked loops",
author = "\{Chalathadka Subrahmanya\}, Shreevathsa and Christian Darsow-Fromm and Oliver Gerberding",
year = "2024",
month = dec,
day = "5",
doi = "10.1109/TIM.2024.3509586",
language = "English",
volume = "74",
journal = "IEEE Transactions on Instrumentation and Measurement",
issn = "0018-9456",
publisher = "Institute of Electrical and Electronics Engineers Inc.",
}
@techreport{557af891fbf54ad4b99a0d15931ed766,
title = "Characterizing seismic isolation using convolutional neural networks and Wiener filters",
abstract = "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 Hz to about 50 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.",
keywords = "Physics - Instrumentation and Detectors, Astrophysics - Instrumentation and Methods for Astrophysics",
author = "Artem Basalaev and Jan-Niklas Feldhusen and Oliver Gerberding",
year = "2024",
month = oct,
day = "18",
doi = "10.48550/arXiv.2410.14806",
language = "English",
series = "arXiv e-prints",
type = "WorkingPaper",
}
@article{eac924a2fefd4c2f8f68b92f0ee4453b,
title = "An analytic, efficient and optimal readout algorithm for compact interferometers based on deep frequency modulation",
abstract = "Compact laser interferometers with large dynamic range are one of the core emerging tools to improve low frequency performance in gravitational wave detectors by providing local displacement sensing with sub 1 pm Hz-0.5 precision. Strong sinusoidal frequency modulations are used in such laser interferometers to create heterodyne-like photodetector signals from which the phase and other parameters, such as the absolute distance, can be extracted. The nested sinusoidal function in such signals is a challenge for the real-time parameter estimation in low-noise applications. In this article, we present an algorithm to calculate exact signal parameters in a non-iterative way from such interferometric signals. The algorithm makes use of a recurrence relation between Bessel functions to enable a direct extraction of modulation parameters from the signal. Additionally, the algorithm is capable of dealing with high phase dynamics where the Doppler-shift of the signal becomes relevant and can limit the range and precision of the parameter estimation, if not accounted for. Simulations show that the algorithm is computationally efficient, can be well parallelised and the phase estimation is close to optimal precision given by the Cramer–Rao lower bound of the signal parameters.",
author = "Tobias Eckhardt and Oliver Gerberding",
year = "2024",
month = sep,
day = "23",
doi = "10.1038/s41598-024-70392-9",
language = "English",
volume = "14",
journal = "Scientific Reports",
issn = "2045-2322",
publisher = "Springer Nature",
number = "1",
}