arXiv subjects

Daniel Brown

Publications and source records attributed to Daniel Brown.

At least 19 recordsLinked to original sources

arXiv2026

A Polarization-Decomposed Method for Simulating Inhomogeneous Birefringence in Laser-Interferometric Gravitational-Wave Detectors

Birefringence in test mass substrates is an emerging limitation for current and future laser-interferometric gravitational-wave detectors, particularly as detectors move toward higher circulating power, cryogenic operation, and crystalline optical materials. Spatially varying birefringence alters both the polarization state and spatial mode content of the intracavity field, reducing interference contrast and coupling into length and alignment control signals. Accurate modeling of these effects is complicated by the fact that most frequency-domain simulation tools employ scalar modal propagation and lack native support for polarization and two-dimensional substrate maps. In this work, we present a practical and general method for simulating inhomogeneous birefringence without modifying existing simulation frameworks. The approach represents the two polarization components as independent scalar fields and introduces their coupling through an equivalent triple-Mach-Zehnder construction that reproduces the Jones matrix of a birefringent medium. We demonstrate the method using realistic birefringence maps of the KAGRA sapphire input test masses. The technique is compatible with any frequency-domain interferometer model and enables efficient birefringence studies for next-generation gravitational-wave detectors.

physics.ins-det↗

arXiv2026

Squeezed state degradations due to mode mismatch and thermal aberrations in gravitational wave detectors

To date, frequency-dependent squeezed light has been used to reduce quantum noise in interferometric gravitational-wave detectors by 6.1 dB (a factor of two). Future upgrades and detectors aim to both reduce quantum noise by 10 dB (a factor of three) and to increase the circulating power in the interferometer arm cavities. Achieving these goals will be extremely challenging due, in part, to the degradations to the squeezed state caused by mode mismatch between the internal interferometer optical cavities and between the auxiliary external cavities. It is therefore imperative to gain a detailed understanding of all sources of mismatch and to obtain experience in mitigating their effects in the current detectors in order to improve astrophysical sensitivity now and in the future. Two types of internal mismatch are identified which are due to the thermal aberrations generated when the test mass optics absorb a small fraction of the circulating arm power. It is found that the dynamics responsible for the degradations caused by the mismatch between the quadratic part of the wavefront of two modes has a characteristic low-pass frequency dependence while the dynamics of the mismatch due to all higher order thermal aberrations has a high-pass behavior. As a consequence, the two types of mismatch are predominantly responsible for different squeezing degradations---some of which are significant for the current detectors and some of which will only be important for future detectors with longer arms. The behavior of these two types of internal mismatch are described, and the implications for detector design, operation, and characterization are discussed.

physics.ins-det↗

arXiv2026

Quantum-Kinetic Dark Energy (QKDE): An effective dark energy framework with a covariantly completed time-dependent scalar kinetic normalization

A minimal effective dark-energy framework - Quantum-Kinetic Dark Energy (QKDE) - is developed in which the scalar kinetic normalization carries a slow background time dependence through a covariantly completed clock field \chi such that K = K(\chi) > 0, while the Einstein-Hilbert metric sector remains unmodified. The resulting effective action admits a diffeomorphism-invariant completion, and working in unitary gauge \chi = t reproduces the background equations used in the numerical analysis. Within the effective field theory of dark energy (EFT-DE) description the model corresponds to \alpha_K > 0 with \alpha_B = \alpha_M = \alpha_T = \alpha_H = 0, implying luminal tensor propagation and a constant Planck mass. Scalar perturbations propagate with c_s^2 = 1, satisfy \Phi = \Psi, and source linear growth through the unmodified Einstein equations. Observable signatures therefore arise solely through the expansion history H(a) and the induced growth D(a). Two realizations of the kinetic normalization are studied: (i) a curvature-motivated form K = 1 + \alpha R/M^2, and (ii) a phenomenological running K = 1 + K_0 (1 + z)^p. A reproducible numerical pipeline and Fisher analysis for H(z), distances, and f\sigma_8(z) are presented. The framework predicts \mu(a,k) = \Sigma(a,k) = 1, \eta(a,k) = 0, and c_T^2 = 1 on linear scales, providing clear falsifiable null tests. Earlier drafts circulated under the working title Scalar-Cost Dark Energy (SCDE).

physics.gen-ph↗

arXiv2025

ProbeMDE: Uncertainty-Guided Active Proprioception for Monocular Depth Estimation in Surgical Robotics

Monocular depth estimation (MDE) provides a useful tool for robotic perception, but its predictions are often uncertain and inaccurate in challenging environments such as surgical scenes where textureless surfaces, specular reflections, and occlusions are common. To address this, we propose ProbeMDE, a cost-aware active sensing framework that combines RGB images with sparse proprioceptive measurements for MDE. Our approach utilizes an ensemble of MDE models to predict dense depth maps conditioned on both RGB images and on a sparse set of known depth measurements obtained via proprioception, where the robot has touched the environment in a known configuration. We quantify predictive uncertainty via the ensemble's variance and measure the gradient of the uncertainty with respect to candidate measurement locations. To prevent mode collapse while selecting maximally informative locations to propriocept (touch), we leverage Stein Variational Gradient Descent (SVGD) over this gradient map. We validate our method in both simulated and physical experiments on central airway obstruction surgical phantoms. Our results demonstrate that our approach outperforms baseline methods across standard depth estimation metrics, achieving higher accuracy while minimizing the number of required proprioceptive measurements. Project page: https://brittonjordan.github.io/probe_mde/

cs.RO↗

arXiv2025

Strain Engineering of Magnetoresistance and Magnetic Anisotropy in CrSBr

Tailoring magnetoresistance and magnetic anisotropy in van der Waals magnetic materials is essential for advancing their integration into technological applications. In this regard, strain engineering has emerged as a powerful and versatile strategy to control magnetism at the two-dimensional (2D) limit. Here, we demonstrate that compressive biaxial strain significantly enhances the magnetoresistance and magnetic anisotropy of few-layer CrSBr flakes. Strain is efficiently transferred to the flakes from the thermal compression of a polymeric substrate upon cooling, as confirmed by temperature-dependent Raman spectroscopy. This strain induces a remarkable increase in the magnetoresistance ratio and in the saturation fields required to align the magnetization of CrSBr along each of its three crystalographic directions, reaching a twofold enhancement along the magnetic easy axis. This enhancement is accompanied by a subtle reduction of the N\'eel temperature by ~10K. Our experimental results are fully supported by first-principles calculations, which link the observed effects to a strain-driven modification in interlayer exchange coupling and magnetic anisotropy energy. These findings establish strain engineering as a key tool for fine-tuning magnetotransport properties in 2D magnetic semiconductors, paving the way for implementation in spintronics and information storage devices.

cond-mat.mtrl-sci↗

arXiv2024

You only thermoelastically deform once: Point Absorber Detection in LIGO Test Masses with YOLO

Current and future gravitational-wave observatories rely on large-scale, precision interferometers to detect the gravitational-wave signals. However, microscopic imperfections on the test masses, known as point absorbers, cause problematic heating of the optic via absorption of the high-power laser beam, which results in diminished sensitivity, lock loss, or even permanent damage. Consistent monitoring of the test masses is crucial for detecting, characterizing, and ultimately removing point absorbers. We present a machine-learning algorithm for detecting point absorbers based on the object-detection algorithm You Only Look Once (YOLO). The algorithm can perform this task in situ while the detector is in operation. We validate our algorithm by comparing it with past reports of point absorbers identified by humans at LIGO. The algorithm confidently identifies the same point absorbers as humans with minimal false positives. It also identifies some point absorbers previously not identified by humans, which we confirm with human follow-up. We highlight the potential of machine learning in commissioning efforts.

astro-ph.IM↗

arXiv2024

Squeezing the quantum noise of a gravitational-wave detector below the standard quantum limit

Precision measurements of space and time, like those made by the detectors of the Laser Interferometer Gravitational-wave Observatory (LIGO), are often confronted with fundamental limitations imposed by quantum mechanics. The Heisenberg uncertainty principle dictates that the position and momentum of an object cannot both be precisely measured, giving rise to an apparent limitation called the Standard Quantum Limit (SQL). Reducing quantum noise below the SQL in gravitational-wave detectors, where photons are used to continuously measure the positions of freely falling mirrors, has been an active area of research for decades. Here we show how the LIGO A+ upgrade reduced the detectors' quantum noise below the SQL by up to 3 dB while achieving a broadband sensitivity improvement, more than two decades after this possibility was first presented.

gr-qc↗

arXiv2024

Angular control noise in Advanced Virgo and implications for the Einstein Telescope

With significantly improved sensitivity, the Einstein Telescope (ET), along with other upcoming gravitational wave detectors, will mark the beginning of precision gravitational wave astronomy. However, the pursuit of surpassing current detector capabilities requires careful consideration of technical constraints inherent in existing designs. The significant improvement of ET lies in the low-frequency range, where it anticipates a one million-fold increase in sensitivity compared to current detectors. Angular control noise is a primary limitation for LIGO detectors in this frequency range, originating from the need to maintain optical alignment. Given the expected improvements in ET's low-frequency range, precise assessment of angular control noise becomes crucial for achieving target sensitivity. To address this, we developed a model of the angular control system of Advanced Virgo, closely matching experimental data and providing a robust foundation for modeling future-generation detectors. Our model, for the first time, enables replication of the measured coupling level between angle and length. Additionally, our findings confirm that Virgo, unlike LIGO, is not constrained by alignment control noise, even if the detector were operating at full power.

astro-ph.IM↗

arXiv2022

Observing the optical modes of parametric instability

Parametric Instability (PI) is a phenomenon that results from resonant interactions between optical and acoustic modes of a laser cavity. This is problematic in gravitational wave interferometers where the high intra-cavity power and low mechanical loss mirror suspension systems create an environment where three mode PI will occur without intervention. We demonstrate a technique for real time imaging of the amplitude and phase of the optical modes of PI yielding the first ever images of this phenomenon which could form part of active control strategies for future detectors.

physics.optics↗

arXiv2022

Continuous gravitational waves in the lab: recovering audio signals with a table-top optical microphone

Gravitational-wave observatories around the world are searching for continuous waves: persistent signals from sources such as spinning neutron stars. These searches use sophisticated statistical techniques to look for weak signals in noisy data. In this paper, we demonstrate these techniques using a table-top model gravitational-wave detector: a Michelson interferometer where sound is used as an analog for gravitational waves. Using signal processing techniques from continuous-wave searches, we demonstrate the recovery of tones with constant and wandering frequencies. We also explore the use of the interferometer as a teaching tool for educators in physics and electrical engineering by using it as an "optical microphone" to capture music and speech. A range of filtering techniques used to recover signals from noisy data are detailed in the Supplementary Material. Here, we present highlights of our results using a combined notch plus Wiener filter and the statistical log minimum mean-square error (logMMSE) estimator. Using these techniques, we easily recover recordings of simple chords and drums, but complex music and speech are more challenging. This demonstration can be used by educators in undergraduate laboratories and can be adapted for communicating gravitational-wave and signal-processing topics to non-specialist audiences.

gr-qc↗

arXiv2021

Hydrodynamic effects on the energy transfer from dipoles to metal slab

A systematic study of nonlocal and size effects on the energy transfer of a dipole (e.g. a molecule or a quantum dot) induced by the proximity of a metal slab is presented. Nonlocal effects are accounted for using the hydrodynamic model (HDM). We derive a general relation that connects the energy transfer rate to the linear charge density-density response function of the slab. This function is explicitly evaluated for the HDM and the local Drude model. We show that a thin metal slab can support a series of higher-frequency surface plasma wave (SPW) modes in addition to the normal SPW modes thanks to the nonlocal effects. These modes markedly alter the response and the energy transfer process, as revealed in the structure of the energy transfer rate in the parameter space. Our findings are important for applications such as the recently developed metal-induced energy transfer imaging, which relies on accurate modeling of the energy transfer rate.

cond-mat.mes-hall↗

arXiv2019

Coupling Rendering and Generative Adversarial Networks for Artificial SAS Image Generation

Acquisition of Synthetic Aperture Sonar (SAS) datasets is bottlenecked by the costly deployment of SAS imaging systems, and even when data acquisition is possible,the data is often skewed towards containing barren seafloor rather than objects of interest. We present a novel pipeline, called SAS GAN, which couples an optical renderer with a generative adversarial network (GAN) to synthesize realistic SAS images of targets on the seafloor. This coupling enables high levels of SAS image realism while enabling control over image geometry and parameters. We demonstrate qualitative results by presenting examples of images created with our pipeline. We also present quantitative results through the use of t-SNE and the Fr\'echet Inception Distance to argue that our generated SAS imagery potentially augments SAS datasets more effectively than an off-the-shelf GAN.

eess.IV↗

arXiv2018

Measuring Human Assessed Complexity in Synthetic Aperture Sonar Imagery Using the Elo Rating System

Performance of automatic target recognition from synthetic aperture sonar data is heavily dependent on the complexity of the beamformed imagery. Several mechanisms can contribute to this, including unwanted vehicle dynamics, the bathymetry of the scene, and the presence of natural and manmade clutter. To understand the impact of the environmental complexity on image perception, researchers have taken approaches rooted in information theory, or heuristics. Despite these efforts, a quantitative measure for complexity has not been related to the phenomenology from which it is derived. By using subject matter experts (SMEs) we derive a complexity metric for a set of imagery which accounts for the underlying phenomenology. The goal of this work is to develop an understanding of how several common information theoretic and heuristic measures are related to the SME perceived complexity in synthetic aperture sonar imagery. To achieve this, an ensemble of 10-meter x 10-meter images were cropped from a high-frequency SAS data set that spans multiple environments. The SME's were presented pairs of images from which they could rate the relative image complexity. These comparisons were then converted into the desired sequential ranking using a method first developed by A. Elo for establishing rankings of chess players. The Elo method produced a plausible rank ordering across the broad dataset. The heuristic and information theoretical metrics were then compared to the image rank from which they were derived. The metrics with the highest degree of correlation were those relating to spatial information, e.g. variations in pixel intensity, with an R-squared value of approximately 0.9. However, this agreement was dependent on the scale from which the spatial variation was measured. Results will also be presented for many other measures including lacunarity, image compression, and entropy.

cs.CV↗

arXiv2015

Fast Simulation of Gaussian-Mode Scattering for Precision Interferometry

Understanding how laser light scatters from realistic mirror surfaces is crucial for the design, com- missioning and operation of precision interferometers, such as the current and next generation of gravitational-wave detectors. Numerical simulations are indispensable tools for this task but their utility can in practice be limited by the computational cost of describing the scattering process. In this paper we present an efficient method to significantly reduce the computational cost of optical simulations that incorporate scattering. This is accomplished by constructing a near optimal representation of the complex, multi-parameter 2D overlap integrals that describe the scattering process (referred to as a reduced order quadrature). We demonstrate our technique by simulating a near-unstable Fabry-Perot cavity and its control signals using similar optics to those installed in one of the LIGO gravitational-wave detectors. We show that using reduced order quadrature reduces the computational time of the numerical simulation from days to minutes (a speed-up of $\approx 2750 \times$) whilst incurring negligible errors. This significantly increases the feasibility of modelling interferometers with realistic imperfections to overcome current limits in state-of-the-art optical systems. Whilst we focus on the Hermite-Gaussian basis for describing the scattering of the optical fields, our method is generic and could be applied with any suitable basis. An implementation of this reduced order quadrature method is provided in the open source interferometer simulation software Finesse.

physics.optics↗

arXiv2013

Interferometer responses to gravitational waves: Comparing FINESSE simulations and analytical solutions

A comparison of analytic calculations and FINESSE simulations of interferometer responses to gravitational wave strain. The response to a gravitational wave is gradually built up from the effect of modulating a space by a gravitational wave to Sagnac and Michelson interferometers with and without arm cavities. This document details the steps necessary to perform such simulations in FINESSE and explicitly derives the interferometer response equations.

physics.optics↗

arXiv2013

Finesse, Frequency domain INterferomEter Simulation SoftwarE

Finesse is a fast interferometer simulation program. For a given optical setup, it computes the light field amplitudes at every point in the interferometer assuming a steady state. To do so, the interferometer description is translated into a set of linear equations that are solved numerically. For convenience, a number of standard analyses can be performed automatically by the program, namely computing modulation-demodulation error signals, transfer functions, shot-noise-limited sensitivities, and beam shapes. Finesse can perform the analysis using the plane-wave approximation or Hermite-Gauss modes. The latter allows computation of the properties of optical systems like telescopes and the effects of mode matching and mirror angular positions.

physics.comp-ph↗

arXiv2013

Phase effects due to beam misalignment on diffraction gratings

All-reflective interferometer configurations have been proposed for the next generation of gravitational wave detectors, with diffractive elements replacing transmissive optics. However, an additional phase noise creates more stringent conditions for alignment stability. A framework for alignment stability with the use of diffractive elements was required using a Gaussian model. We successfully create such a framework involving modal decomposition to replicate small displacements of the beam (or grating) and show that the modal model does not contain the phase changes seen in an otherwise geometric planewave approach. The modal decomposition description is justified by verifying experimentally that the phase of a diffracted Gaussian beam is independent of the beam shape, achieved by comparing the phase change between a zero-order and first-order mode beam. To interpret our findings we employ a rigorous time-domain simulation to demonstrate that the phase changes resulting from a modal decomposition are correct, provided that the coordinate system which measures the phase is moved simultaneously with the effective beam displacement. This indeed corresponds to the phase change observed in the geometric planewave model. The change in the coordinate system does not instinctively occur within the analytical framework, and therefore requires either a manual change in the coordinate system or an addition of the geometric planewave phase factor.

physics.optics↗

arXiv2013

Realistic polarizing Sagnac topology with DC readout for the Einstein Telescope

The Einstein Telescope (ET) is a proposed future gravitational wave detector. Its design is original, using a triangular orientation of three detectors and a xylophone configuration, splitting each detector into one high-frequency and one low-frequency system. In other aspects the current design retains the dual-recycled Michelson interferometer typical of current detectors, such as Advanced LIGO. In this paper, we investigate the feasibility of replacing the low-frequency part of the ET detectors with a Sagnac interferometer. We show that a Sagnac interferometer, using realistic optical parameters based on the ET design, could provide a similar level of radiation pressure noise suppression without the need for a signal recycling mirror and the extensive filter cavities. We consider the practical issues of a realistic, power-recycled Sagnac, using linear arm cavities and polarizing optics. In particular, we investigate the effects of nonperfect polarizing optics and propose a new method for the generation of a local oscillator field similar to the DC readout scheme of current detectors.

physics.ins-det↗