Triaxial optomechanical accelerometers offer compact, ground-testable alternatives to electrostatic sensors for satellite geodesy, seismometry, and various other applications. We demonstrate a low-CSWaP triaxial sensor using monolithic fused-silica resonators with dual heterodyne interferometric readout. The X axis reaches a 60 pico-g/√(Hz) readout noise floor, and the in-plane axes resolve ambient seismic ground motion in agreement with a co-located commercial seismometer from 4 mHz to 8 Hz. The Z axis exhibits higher noise under 1g loading due to gravity-induced geometric stiffening (44.45 Hz versus 11.07 Hz in a 0g-equivalent configuration), with measurements indicating in-orbit performance on par with the in-plane sensors. These results support the feasibility of triaxial optomechanical accelerometry for space missions and ground-based applications.

ODIN (Optomechanical Distributed Instrument for Inertial Sensing and Navigation) is a novel low-frequency optomechanical inertial sensing system funded under NASA’s InVEST program for space technology demonstration. The instrument employs twelve uniaxial fused silica optomechanical accelerometers arranged in a gyroscope-free cubic configuration, enabling simultaneous recovery of linear acceleration, angular acceleration, and centripetal terms. ODIN targets sensitivities of $\sim {10^{ - 10}}{\text{m}}{{\text{s}}^{ - 2}}/\sqrt {{\text{Hz}}} $ and $7 \times {10^{ - 10}}{\text{rad}}{{\text{s}}^{ - 2}}/\sqrt {{\text{Hz}}} $ at 10 mHz for linear and angular acceleration, respectively. ODIN will fly as a secondary payload aboard the GRATTIS (Gravitational Reference Advanced Technology Test in Space) mission, scheduled for launch in early 2027, representing a significant step toward compact, cost-effective space-based accelerometry for future Earth geodesy and inertial navigation applications.

Parasitic interference is a common limitation in laser interferometers, arising from unwanted beams that corrupt the phase measurement and degrade displacement sensitivity. In this work, we present a unified framework for the characterization and mitigation of parasitic interference in heterodyne interferometers. Parasitic beams are classified into two types based on the orientation of their corresponding phase vectors, and their noise contribution is modeled as a function of polarization, relative amplitude, and phase of the parasitic beam. Central to this framework is the concept of coupling coefficients, which quantify the interferometer's susceptibility to parasitic interference and can be readily computed using Jones calculus for any optical configuration. The two types of parasitic interference motivate distinct mitigation strategies: differential interferometry and balanced detection, complemented by polarization control and high-quality beam splitters. The models and mitigation strategies are validated experimentally in both a simplified Mach-Zehnder interferometer and a differential interferometer used for optomechanical inertial sensing, demonstrating reductions in parasitic phase noise by up to four orders of magnitude and achieving sub-picometer displacement sensitivity at frequencies as low as 9 mHz under ambient atmospheric pressure.

We present the construction and characterization of a system of two optomechanical accelerometers used as a gravity gradiometer unit. The unit is sensitive to accelerations along a single axis, which drive a single mode of each accelerometer. The excited mode is linear and uniaxial and can be read out via a single interferometric measurement. High mechanical quality factors on the order of 5 x 10(5) and continued development of novel high sensitivity interferometers have allowed us to achieve sensor noise floors at sub-picometer displacements, which correspond to an acceleration noise floor of 1.7x10(-9) ms(-)2/root Hz at 1 Hz. The mechanical accelerometers have a theoretical thermal noise floor of 1x10(-14) m/root Hz at 1 Hz, and noise attributable to the optical readout has been the primary limit of our sensors. We have designed our sensors to be sensitive in the band of 10 mu Hz to 1 Hz with the fundamental mode of our accelerometers typically between 5-10 Hz. In this frequency band we are sensitive to several noise sources including laser frequency noise, environmental temperature and pressure fluctuations, non-linear optical path difference (OPD) fiber noise, laser random intensity noise (RIN), electronic noise, and seismic noise, among others. The seismic signal is of note, as systems agree well with commercial seismometers, showing that we are limited by seismic signal above 10 mHz in all on ground measurements with our sensors. The sections of this paper will cover the mechanical design of our gradiometer sensor head, the optical design of our interferometric readout system, and the noise contributions of several mechanisms along with mitigation/correction efforts for each effect.

We present a theoretical and numerical investigation of a novel photonic integrated optomechanical accelerometer, which utilizes the elasto-optic effect in a silicon nitride racetrack resonator for precise motion detection. The study combines finite-element analysis using COMSOL Multiphysics, coupling structural mechanics, wave optics at telecom wavelengths, and heat transfer in solids to estimate key performance metrics based on realistic material parameters. We estimate an optomechanical coupling constant of 0.8 MHz per nanometer, along with high mechanical and optical quality factors. Our predictions indicate a shot noise-limited displacement resolution at the femtometer level, and acceleration noise floors below 300 nano-g across a 15 kHz bandwidth. These results represent a state-of-the-art performance, placing this proposed accelerometer among the best integrated optomechanical accelerometers with comparable bandwidth and footprint.

The optical truss interferometer (OTI) is a contingent subsystem proposed for the LISA telescopes to aid in the verification of a 1pmHz optical path length stability. Each telescope would be equipped with three pairs of compact fiber-coupled units, each forming an optical cavity with a baseline proportional to the telescope length at different points around the aperture. Employing a Pound-Drever-Hall approach to maintain a modulated laser field on resonance with each cavity, the dimensional stability of the telescope can be measured and verified. We have designed and developed prototype OTI units to demonstrate the capability of measuring stable structures, such as the LISA telescope, with a 1pmHz sensitivity using a set of freely mountable fiber-injected cavities. Aside from its initial motivation for the telescope, the OTI can also be readily integrated with other systems to aid in ground testing experiments. In this paper, we outline our experimental setup, measurement results, and analyses of the noise limitations.

We present the results of a search for gravitational-wave transients associated with core-collapse supernova SN 2023ixf, which was observed in the galaxy Messier 101 via optical emission on 2023 May 19, during the LIGO–Virgo–KAGRA 15th Engineering Run. We define a five-day on-source window during which an accompanying gravitational-wave signal may have occurred. No gravitational waves have been identified in data when at least two gravitational-wave observatories were operating, which covered ∼14% of this five-day window. We report the search detection efficiency for various possible gravitational-wave emission models. Considering the distance to M101 (6.7 Mpc), we derive constraints on the gravitational-wave emission mechanism of core-collapse supernovae across a broad frequency spectrum, ranging from 50 Hz to 2 kHz, where we assume the gravitational-wave emission occurred when coincident data are available in the on-source window. Considering an ellipsoid model for a rotating proto-neutron star, our search is sensitive to gravitational-wave energy 1 × 10 −4 M ⊙ c 2 and luminosity 2.6 × 10 −4 M ⊙ c 2 s −1 for a source emitting at 82 Hz. These constraints are around an order of magnitude more stringent than those obtained so far with gravitational-wave data. The constraint on the ellipticity of the proto-neutron star that is formed is as low as 1.08, at frequencies above 1200 Hz, surpassing past results.

We present results from a search for X-ray/gamma-ray counterparts of gravitational-wave (GW) candidates from the third observing run (O3) of the LIGO-Virgo-KAGRA network using the Swift Burst Alert Telescope (Swift-BAT). The search includes 636 GW candidates received with low latency, 86 of which have been confirmed by the offline analysis and included in the third cumulative Gravitational-Wave Transient Catalogs (GWTC-3). Targeted searches were carried out on the entire GW sample using the maximum-likelihood Non-imaging Transient Reconstruction and Temporal Search pipeline on the BAT data made available via the GUANO infrastructure. We do not detect any significant electromagnetic emission that is temporally and spatially coincident with any of the GW candidates. We report flux upper limits in the 15-350 keV band as a function of sky position for all the catalog candidates. For GW candidates where the Swift-BAT false alarm rate is less than 10(-3) Hz, we compute the GW-BAT joint false alarm rate. Finally, the derived Swift-BAT upper limits are used to infer constraints on the putative electromagnetic emission associated with binary black hole mergers.

In this work a method for using accelerometers for the determination of angular velocity and acceleration is presented. Minimum sensor requirements and insights into how an array of accelerometers can be configured to maximize estimator performance are considered. The framework presented utilizes linear least squares to estimate functions that are quadratic in angular velocity. Simple methods for determining the sign of the spin axis and the linearized covariance approximation are presented and found to perform quite effectively when compared to results obtained by Monte Carlo.

We present a laser frequency stabilization system based on an iodine-filled hollow-core photonic microcell (PMC), which is a sealed version of a hollow-core photonic crystal fiber (HC-PCF). A 532 nm laser is locked to the a1 component of the R(56) 32-0 transition of molecular iodine in the fiber cell, and its frequency stability is compared to that of the same component in a free-space iodine cell. Noise analysis reveals that the system is limited by parasitic beams that interfere with the beam of interest and degrade the error signal. We have identified and characterized three types of parasitic interference and designed suppression methods for each. After applying these suppression methods, the frequency stability improved by more than an order of magnitude. The system achieves fractional frequency stability of 3.5 × 10 −13 for integration times around 1000 s. To our knowledge, this represents the best frequency stability achieved using a gas-filled hollow-core photonic crystal fiber frequency reference.

The LISA Pathfinder (LPF) mission successfully demonstrated the feasibility of the technology needed for the future space borne gravitational wave observatory LISA. A key subsystem under study was the laser interferometer, which measured the changes in relative distance in between two test masses (TMs). It achieved a sensitivity of 32.0 thorn 2.4 -1.7 fm=ffiffiffiffiffiA/Hz, which was significantly better than the prelaunch tests. This improved performance allowed direct observation of the influence of laser frequency noise in the readout. The differences in optical path lengths between the measurement and reference beams in the individual interferometers of our setup determined the level of this undesired readout noise. Here, we discuss the dedicated experiments performed on LPF to measure these differences with high precision. We reached differences in path length difference between (368 +/- 5) mu m and (329.6 +/- 0.9) mu m which are significantly below the required level of 1 mm or 1000 mu m. These results are an important contribution to our understanding of the overall sensor performance. Moreover, we observed varying levels of laser frequency noise over the course of the mission. We provide evidence that these do not originate from the laser frequency stabilization scheme which worked as expected. Therefore, this frequency stabilization would be applicable to other missions with similar laser frequency stability requirements.

We present Fermi Gamma-ray Burst Monitor (Fermi-GBM) and Swift Burst Alert Telescope (Swift-BAT) searches for gamma-ray/X-ray counterparts to gravitational wave (GW) candidate events identified during the third observing run of the Advanced LIGO and Advanced Virgo detectors. Using Fermi-GBM on-board triggers and sub-threshold gamma-ray burst (GRB) candidates found in the Fermi-GBM ground analyses, the Targeted Search and the Untargeted Search, we investigate whether there are any coincident GRBs associated with the GWs. We also search the Swift-BAT rate data around the GW times to determine whether a GRB counterpart is present. No counterparts are found. Using both the Fermi-GBM Targeted Search and the Swift-BAT search, we calculate flux upper limits and present joint upper limits on the gamma-ray luminosity of each GW. Given these limits, we constrain theoretical models for the emission of gamma-rays from binary black hole mergers.

Low-frequency and 1/f noise are common measurement limitations that arise in a variety of physical processes. Mitigation methods for these noises are dependent on their source. Here, we present a method for removing 1/f noise of optical origin using a micro-cavity Fabry–Pérot (FP) interferometer. A mechanical modulation of the FP cavity length was applied to a previously studied opto-mechanical sensor. It effectively mimics an up-conversion of the laser frequency, shifting signals to a region where lower white-noise sources dominate and 1/f noise is not present. Demodulation of this signal shifts the results back to the desired frequency range of observation with the reduced noise floor of the higher frequencies. This method was found to improve sensitivities by nearly two orders of magnitude at 1 Hz and eliminated 1/f noise in the range from 1 Hz to 4 kHz. A mathematical model for low-finesse FP cavities is presented to support these results. This study suggests a relatively simple and efficient method for 1/f noise suppression and improving the device sensitivity of systems with an FP interferometer readout.

We report on the progress of our novel low-frequency optomechanical inertial sensing technologies for gravimetry, accelerometry and seismometry on ground, space and planetary applications. Our technologies are designed to be compact, portable, and are comprised of monolithically fabricated mechanical resonators that incorporate compact and highly sensitive laser interferometric displacement sensors. Current laboratory prototypes have demonstrated mechanical quality factors Q of 4.77x105, an mQ-product above 1200 kg, a fundamental mechanical resonance of 4.7 Hz, which highlight their high sensitivity with acceleration noise floor nears 1x10-11 m s-2/√Hz. Such compact systems are excellent candidates for portable and deployable systems on compact and low SWaP platforms and flight payloads. A prototype packaging has been developed to reduce losses caused by typical mechanical mounts. We have conducted comparison measurements with commercial low-frequency systems to an excellent agreement. Recent measurements taken with the resonator mounted in this packaging atop a vibration isolation platform have indicated that our system is seismically limited above 1 mHz. Noise floors in the order of 82 pico-g/√Hz at 0.4 Hz has been demonstrated in our laboratory. We will present recent updates on our optomechanical inertial sensors, including up to date measurements of the resonator and interferometer sensitivity, as well as that of the combined system.

Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass $M>70$ $M_\odot$) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities $0 < e \leq 0.3$ at $0.33$ Gpc$^{-3}$ yr$^{-1}$ at 90\% confidence level.

The magnetar SGR 1935+2154 is the only known Galactic source of fast radio bursts (FRBs). FRBs from SGR 1935+2154 were first detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME)/FRB and the Survey for Transient Astronomical Radio Emission 2 in 2020 April, after the conclusion of the LIGO, Virgo, and KAGRA Collaborations' O3 observing run. Here, we analyze four periods of gravitational wave (GW) data from the GEO600 detector coincident with four periods of FRB activity detected by CHIME/FRB, as well as X-ray glitches and X-ray bursts detected by NICER and NuSTAR close to the time of one of the FRBs. We do not detect any significant GW emission from any of the events. Instead, using a short-duration GW search (for bursts <= 1 s) we derive 50% (90%) upper limits of 10(48) (10(49)) erg for GWs at 300 Hz and 10(49) (10(50)) erg at 2 kHz, and constrain the GW-to-radio energy ratio to <= 10(14)-10(16). We also derive upper limits from a long-duration search for bursts with durations between 1 and 10 s. These represent the strictest upper limits on concurrent GW emission from FRBs.

Magnetars are neutron stars with exceptionally strong dipole magnetic fields which are observed to display a range of x-ray flaring behavior, but the flaring mechanism is not well understood. The third observing run of Advanced LIGO and Virgo extended from April 1, 2019 to March 27, 2020, and contained x-ray flares from known magnetar SGR 1935+2154, as well as the newly-discovered magnetar, Swift J1818-1607. We search for gravitational waves coincident with these magnetar flares with minimally modeled, coherent searches which specifically target both short-duration gravitational waves produced by excited f-modes in the magnetar's core, as well as long-duration gravitational waves motivated by the Quasi-Periodic Oscillations observed in the tails of giant flares. In this paper, we report on the methods and sensitivity estimates of these searches, and the astrophysical implications.

This paper investigates state estimation methods for dynamical systems when model evaluations are performed on resource-constrained embedded systems with finite precision compute elements. Minimum mean square estimation algorithms are reformulated to incorporate finite-precision numerical errors in states, inputs, and measurements. Quantized versions of least squares batch estimation, sequential Kalman, and square-root filtering algorithms are proposed for fixed-point implementations. Numerical simulations are used to demonstrate performance improvements over standard filter formulations. Steady-state covariance analysis is employed to capture the performance trade-offs with numerical precision, providing insights into the best possible filter accuracy achievable for a given numerical representation. A low-latency fixed-point acceleration state estimation architecture for optomechanical sensing applications is realized on Field Programmable Gate Array System on Chip (FPGA-SoC) hardware. The hardware implementation results of the estimator are compared with double-precision MATLAB implementation, and the performance metrics are reported. Simulations and the experimental results underscore the significance of modeling quantization errors into state estimation pipelines for fixed-point embedded implementations.

We present ODIN, an Optomechanical-Distributed instrument for Inertial sensing and Navigation system. ODIN is a novel instrument that has been funded under NASA’s InVEST program as technology demonstration program in space, to fly as a secondary payload on the GRATTIS mission led by the University of Florida. ODIN is an instrument of low cost, size, weight, and power (CSWaP), and utilizes arrays of in-plane dual-accelerometer systems that are capable of providing linear acceleration and angular measurements at levels of 10^-9 ms^-2/√Hz and 50 µrad/√Hz, respectively, which are relevant for mass change.Accelerometry has become crucial for monitoring mass change within the Earth system. Novel optomechanical inertial sensors provide an alternative instrument to existing ones, exhibiting lower cost, size, weight and power (CSWaP) with performances on par with GRACE. Reduced CSWaP makes these instruments suitable for enhancing mission reliability as redundant accelerometers, and can also improve science data quality by providing measurements of thruster firings and transient effects, among others.Moreover, low CSWaP optomechanical instruments would enable cost-effective mission designs, spacecraft miniaturization, simplified architectures, as well as the deployment of constellations of satellite pairs flying at lower altitudes, and observations of transient phenomena that may impact mission performance.We will discuss some of the potential science cases that can be addressed with this technology, as well as current status and development timeline of this flight instrument.