arXiv subjects

Takayuki Tomaru

Publications and source records attributed to Takayuki Tomaru.

At least 19 recordsLinked to original sources

arXiv2025

Proof-of-principle demonstration of a Polarization-Circulation Speed Meter

We present the first experimental implementation of a polarization-circulation speed meter. In our experiment, the interferometer was reduced to a single-cavity configuration with all mirrors fixed. A green-locking scheme was employed to stabilize the polarization circulation cavity, and a lock-acquisition procedure was demonstrated to realize speed-meter operation. The system was characterized by measuring the transfer function from a pseudo-displacement signal to the photodetector output, confirming that the device measures the speed of mirror motion. These results support the feasibility of polarization-circulation speed meters and suggest that the control scheme could be extended to more complex configurations, such as Michelson interferometers and suspended-mirror systems.

quant-ph↗

arXiv2025

Photon Calibration Performance of KAGRA during the 4th Joint Observing Run (O4)

KAGRA is a kilometer-scale cryogenic gravitational-wave (GW) detector in Japan. It joined the 4th joint observing run (O4) in May 2023 in collaboration with the Laser Interferometer GW Observatory (LIGO) in the USA, and Virgo in Italy. After one month of observations, KAGRA entered a break period to enhance its sensitivity to GWs, and it is planned to rejoin O4 before its scheduled end in October 2025. To accurately recover the information encoded in the GW signals, it is essential to properly calibrate the observed signals. We employ a photon calibration (Pcal) system as a reference signal injector to calibrate the output signals obtained from the telescope. In ideal future conditions, the uncertainty in Pcal could dominate the uncertainty in the observed data. In this paper, we present the methods used to estimate the uncertainty in the Pcal systems employed during KAGRA O4 and report an estimated system uncertainty of 0.79%, which is three times lower than the uncertainty achieved in the previous 3rd joint observing run (O3) in 2020. Additionally, we investigate the uncertainty in the Pcal laser power sensors, which had the highest impact on the Pcal uncertainty, and estimate the beam positions on the KAGRA main mirror, which had the second highest impact. The Pcal systems in KAGRA are the first fully functional calibration systems for a cryogenic GW telescope. To avoid interference with the KAGRA cryogenic systems, the Pcal systems incorporate unique features regarding their placement and the use of telephoto cameras, which can capture images of the mirror surface at almost normal incidence. As future GW telescopes, such as the Einstein Telescope, are expected to adopt cryogenic techniques, the performance of the KAGRA Pcal systems can serve as a valuable reference.

astro-ph.IM↗

arXiv2024

Theoretical Characteristics of a three-point Roberts Linkage

The Roberts linkage is recognized for enabling long-period pendulum motion in a compact format. Utilizing this characteristic, we are developing a three-point Roberts linkage for vibration isolation systems, with an eye towards its potential contribution to the development of next-generation interferometric gravitational wave antennas. In this article, we derived the equations to determine the essential parameters when using this linkage as a vibration isolation system, namely the equivalent pendulum length and the relationship between translational motion of the center of mass and rigid body rotation, from size parameters. Additionally, we analyzed the behavior in response to various errors.

physics.ins-det↗

arXiv2023

Control Scheme for Polarization Circulation Speed Meter Using a Dual-Retardation Waveplate

In interferometric gravitational wave detectors, quantum radiation pressure noise, which is a back action of the measurement, will limit their sensitivities at low frequencies. Speed meters are one of the solutions to reduce the back action noise and improve the sensitivities, and furthermore, they can surpass the standard quantum limit over a wide range of frequencies. The Polarization Circulation Speed Meter is the latest incarnation of the speed meter concept in the sense that it requires a slight modification in the conventional interferometer designs; however, its control scheme has not been developed. The main difficulty is the length and alignment control of the cavity formed by the polarization circulation mirror and the input test masses, whose round-trip phase shift should be kept to $π$. In this article, we propose a new control scheme using a dual-retardation waveplate, called Dual-Retardance Control (DRC). In addition, we compare the shot noise level of the DRC to another simpler scheme by dithering. Finally, we design the experimental setup for the demonstration of the DRC and show the expected results through the transfer function measurement.

gr-qc↗

arXiv2023

Development of epoxy-based millimeter absorber with expanded polystyrenes and carbon black

We recently developed and characterized an absorber for millimeter wavelengths. To absorb the millimeter wave efficiently, we need to develop the low reflection and high absorption material. To meet these requirements, we tried to add polystyrene beads in the epoxy for multi-scattering in the absorber. The typical diameter of polystyrene beads corresponds to the scale of Mie scattering for the multi-scattering of photons in the absorber. The absorber consists of epoxy, carbon black, and expanded polystyrene beads. The typical size of the expanded polystyrene beads is consistent with the peak of cross-section of Mie scattering to increase the mean free path in the absorber. By applying this effect, we succeeded in improving the performance of the absorber. In this paper, we measured the optical property of epoxy for the calculation of the Mie scattering effect. Based on the calculation result, we developed the 8 types samples by changing the ratio of absorber material. To compare 8 samples, we characterized the reflectance and transmittance of the absorber in millimeter length. The measured reflectance and transmittance of 2 mm thickness sample with optimized parameter are less than 20% and 10%. We also measured the transmittance in sub-millimeter wavelength. The measured transmittance is less than 1%. The shape of absorber can be modified for any shape, such as chip and pyramidal shapes. By using this absorber, we can apply for the mitigation of stray light of millimeter wave telescope with any shapes.

astro-ph.IM↗

arXiv2022

Estimation of Newtonian noise from KAGRA cooling system

KAGRA is the first km-scale gravitational wave detector to be constructed underground and employ cryogenics to cool down its test masses. While the underground location provides a quiet site with low seismic noise, the cooling infrastructure is known to generate large mechanical vibrations due to cryocooler operation and structural resonances of the cryostat. As cooling system components are relatively heavy and in close proximity to the test masses, oscillation of gravity force induced by their vibration, so-called Newtonian noise, could contaminate the detector sensitivity. In this paper, we use the results from vibration analysis of the KAGRA cryostat to estimate cooling system Newtonian noise in the 1-100 Hz frequency band. Our calculations show that, while this noise does not limit the current detector sensitivity or inspiral range, it will be an issue in the future when KAGRA improves its sensitivity. We conclude that KAGRA may need to implement Wiener filters to subtract this noise in the future.

physics.ins-det↗

arXiv2022

A laser interferometer accelerometer for vibration sensitive cryogenic experiments

Monitoring motion originating from ultra low-temperature cooling systems like cryocoolers is important for vibration sensitive cryogenic experiments like KAGRA. Since no commercial cryogenic accelerometers are available, we developed a compact self-calibrating accelerometer with a Michelson interferometer readout for cryogenic use. Change in calibration factor and drop in interferometer output originating from temperature drop were the main concerns which were tackled. Sensitivity of $3.38\times10^{-11}$ m/$\sqrt{\mathrm{Hz}}$ at 1 Hz was achieved at 300 K. The accelerometer was tested inside the KAGRA cryostat; showed stable operation down to 12 K in 0.1-100 Hz band with only 1% visibility drop. Our accelerometer can be employed in low vibration cryogenic environment for a multitude of applications.

physics.ins-det↗

arXiv2022

Vibration Analysis of KAGRA Cryostat at Cryogenic Temperature

KAGRA uses cryogenics to cool its sapphire test masses down to 20 K to reduce the thermal noise. However, cryocooler vibration and structural resonances of the cryostat couple to test mass and can contaminate the detector sensitivity. We performed vibration analysis of the cooling system at cryogenic temperature to study its impact on detector sensitivity. Our measurement show shield vibration below 1 Hz is not impacted by cryocooler operation or structural resonances and follows ground motion. The noise floor of the shield in 1-100 Hz was observed to be 2-3 order of magnitude larger than seismic motion even without cryocooler operation. The operation of cryocoolers does not change the noise floor, but 2.0 Hz peaks and their harmonics were observed over the entire spectrum (1-100 Hz). These results were used to calculate the coupling of cooling system vibration to the test mass. We conclude that vibration from the cooling system does not limit KAGRA design sensitivity.

physics.ins-det↗

arXiv2021

Cryogenic suspension design for a kilometer-scale gravitational-wave detector

We report the mirror suspension design for Large-scale Cryogenic Gravitational wave Telescope, KAGRA, during bKAGRA Phase 1. Mirror thermal noise is one of the fundamental noises for room-temperature gravitational-wave detectors such as Advanced LIGO and Advanced Virgo. Thus, reduction of thermal noise is required for further improvement of their sensitivity. One effective approach for reducing thermal noise is to cool the mirrors. There are many technical challenges that must be overcome to cool the mirrors, such as cryocooler induced vibrations, thermal drift in suspensions, and reduction in duty cycling due to the increased number of potential failure mechanisms. Our mirror suspension has a black coating that makes radiative cooling more efficient. For conduction cooling, we developed ultra high purity aluminum heat links, which yield high thermal conductivity while keeping the spring constant sufficiently small. A unique inclination adjustment system, called moving mass, is used for aligning the mirror orientation in pitch. Photo-reflective displacement sensors, which have a large range, are installed for damping control on marionette recoil mass and intermediate recoil mass. Samarium cobalt magnets are used for coil-magnet actuators to prevent significant change of magnetism between room temperature and cryogenic temperature. In this paper, the design of our first cryogenic payload and its performance during bKAGRA Phase 1 are discussed.

physics.ins-det↗

arXiv2020

High Performance Heat Conductor with Small Spring Constant for Cryogenic Applications

We developed a soft and high thermal conductive heat link for cryogenic applications. The measured maximum thermal conductivity was approximately 18500 W/m/K at 10 K. This spring constant was 1/43 of that of a single thick wire with the same cross-sectional area at room temperature. We realized these performances by utilizing high purity aluminum (99.9999 %, 6N) and by stranding many thin wires that are 0.15 mm in diameter. The electrical Residual Resistivity Ratio (RRR) was also measured and used to estimate the thermal conductivity by Wiedemann-Franz law. We observed the size effect on the electrical conductivity, and evaluated the effect of mechanical deformation to the RRR. These evaluations allow us to design a pragmatic heat link for cryogenic application.

physics.ins-det↗

arXiv2019

Mirror actuation design for the interferometer control of the KAGRA gravitational wave telescope

KAGRA is a 3-km cryogenic interferometric gravitational wave telescope located at an underground site in Japan. In order to achieve its target sensitivity, the relative positions of the mirrors of the interferometer must be finely adjusted with attached actuators. We have developed a model to simulate the length control loops of the KAGRA interferometer with realistic suspension responses and various noises for mirror actuation. Using our model, we have designed the actuation parameters to have sufficient force range to acquire lock as well as to control all the length degrees of freedom without introducing excess noise.

physics.ins-det↗

arXiv2018

Molecular adsorbed layer formation on cooled mirrors and its impacts on cryogenic gravitational wave telescopes

Cryogenic mirrors have been introduced to the KAGRA gravitational wave telescope in Japan, and are also planned to be used in next-generation gravitational wave telescopes to further improve their sensitivity. Molecular gases inside vacuum chambers adhere to cold mirror surfaces because they lose their kinetic energy when they hit cryogenic surfaces. Finally, a number of adsorbed molecules form an adlayer, which will grow with time. The growing adlayer functions as an optical coating and changes the properties of the underlying mirror, such as reflectance, transmittance, and absorption, which are carefully chosen to maximize the detector sensitivity. The adlayer possibly affects the gravitational wave detector sensitivity. In order to characterize these changes, a high-finesse Fabry--Perot cavity was introduced to a KAGRA cryostat and the finesse of the cavity was monitored for 35 days under cryogenic conditions. We confirmed that the molecular adlayer was formed on a cold mirror and caused an oscillation in the finesse. The real and imaginary parts of the refractive index of the adlayer were $1.26 \pm 0.073$ and $2.2 \times 10^{-7} \pm 1.3 \times 10^{-7} $, respectively. These are considered to be that of $\mathrm{H_2O}$ molecules. The formation rate of the molecular adlayer was 27 $\pm$ 1.9 $\mathrm{nm/day}$. In this paper, we describe theoretical and experimental studies of the formation of a molecular adlayer on cryogenic mirrors. Furthermore, the effects of a molecular adlayer on the quantum noise and the input heat to the test mass are also discussed.

gr-qc↗

arXiv2018

Improving the absolute accuracy of the gravitational wave detectors by combining the photon pressure and gravity field calibrators

The absolute accuracy of the estimated parameters of gravitational wave sources will be fundamentally limited by the calibration uncertainties of the detectors in upcoming observation runs with the increased number of source statistics. Photon calibrators have so far been the primary tools for absolute calibration of test-mass displacement, relying on measurement of the photon pressure. The current technological limit of the absolute calibration uncertainty for gravitational-wave amplitudes is limited to a few percent, due to the uncertainty in the laser power-standard maintained by the metrology institutes. To reduce this uncertainty, this article proposes a novel calibration method that combines a photon calibrator and a gravity field calibrator. The gravity field calibrator achieves modulation of the displacement of the test mass by generating a gravity gradient. In previous studies, uncertainty in the distance between the test mass and the gravity field calibrator has proven a serious source of systematic error. To suppress this uncertainty, we propose a novel method that uses a combination of quadrupole and hexapole mass distributions in the gravity field calibrator. We estimate the absolute uncertainty associated with method to be as low as 0.17~%, which is ten times less than that of previous methods.

astro-ph.IM↗

arXiv2016

Two-layer anti-reflection coating with mullite and polyimide foam for large-diameter cryogenic infrared filters

We have developed a novel two-layer anti-reflection (AR) coating method for large-diameter infrared (IR) filters made of alumina, for the use at cryogenic temperatures in millimeter wave measurements. Thermally- sprayed mullite and polyimide foam (Skybond Foam) are used as the AR material. An advantage of the Skybond Foam is that the index of refraction is chosen between 1.1 and 1.7 by changing the filling factor. Combination with mullite is suitable for wide-band millimeter wave measurements with sufficient IR cutoff capability. We present the material properties, fabrication of a large-diameter IR filter made of alumina with this AR coating method, and characterizations at cryogenic temperatures. This technology can be applied to a low-temperature receiver system with a large-diameter focal plane for next-generation cosmic microwave background (CMB) polarization measurements, such as POLARBEAR-2 (PB-2).

astro-ph.IM↗

arXiv2016

POLARBEAR Constraints on Cosmic Birefringence and Primordial Magnetic Fields

We constrain anisotropic cosmic birefringence using four-point correlations of even-parity $E$-mode and odd-parity $B$-mode polarization in the cosmic microwave background measurements made by the POLARization of the Background Radiation (POLARBEAR) experiment in its first season of observations. We find that the anisotropic cosmic birefringence signal from any parity-violating processes is consistent with zero. The Faraday rotation from anisotropic cosmic birefringence can be compared with the equivalent quantity generated by primordial magnetic fields if they existed. The POLARBEAR nondetection translates into a 95% confidence level (C.L.) upper limit of 93 nanogauss (nG) on the amplitude of an equivalent primordial magnetic field inclusive of systematic uncertainties. This four-point correlation constraint on Faraday rotation is about 15 times tighter than the upper limit of 1380 nG inferred from constraining the contribution of Faraday rotation to two-point correlations of $B$-modes measured by Planck in 2015. Metric perturbations sourced by primordial magnetic fields would also contribute to the $B$-mode power spectrum. Using the POLARBEAR measurements of the $B$-mode power spectrum (two-point correlation), we set a 95% C.L. upper limit of 3.9 nG on primordial magnetic fields assuming a flat prior on the field amplitude. This limit is comparable to what was found in the Planck 2015 two-point correlation analysis with both temperature and polarization. We perform a set of systematic error tests and find no evidence for contamination. This work marks the first time that anisotropic cosmic birefringence or primordial magnetic fields have been constrained from the ground at subdegree scales.

astro-ph.CO↗

arXiv2014

Cryogenic infrared filter made of alumina for use at millimeter wavelength

We propose a high thermal conductivity infrared (IR) filter using alumina for use in millimeter wave detection systems. We constructed a prototype two-layer anti-reflection (AR) coated alumina filter with a diameter of 100mm and a thickness of 2mm, and characterized its thermal and optical properties. The transmittance of this filter at 95GHz and 150GHz is 97% and 95% while the estimated 3dB cutoff frequency is at 450GHz. The high thermal conductivity of alumina minimizes thermal gradients. We measure a differential temperature of only 0.21K between the center and the edge of the filter when it is mounted on a thermal anchor of 77K. We also constructed a thermal model based on the prototype filter and analyzed the scalability of the filter diameter. We conclude that temperature increase at the center of alumina IR filter is less than 6K even with a large diameter of 500mm, when the temperature at the edge of the filter is 50K. This is suitable for an application to a large-throughput next-generation cosmic microwave background (CMB) polarization experiment, such as POLARBEAR-2 (PB-2).

astro-ph.IM↗

arXiv2013

Adaptation of frequency-domain readout for Transition Edge Sensor bolometers for the POLARBEAR-2 Cosmic Microwave Background experiment

The POLARBEAR-2 CosmicMicrowave Background (CMB) experiment aims to observe B-mode polarization with high sensitivity to explore gravitational lensing of CMB and inflationary gravitational waves. POLARBEAR-2 is an upgraded experiment based on POLARBEAR-1, which had first light in January 2012. For POLARBEAR-2, we will build a receiver that has 7,588 Transition Edge Sensor (TES) bolometers coupled to two-band (95 and 150 GHz) polarization-sensitive antennas. For the large array's readout, we employ digital frequency-domain multiplexing and multiplex 32 bolometers through a single superconducting quantum interference device (SQUID). An 8-bolometer frequency-domain multiplexing readout has been deployed on POLARBEAR-1 experiment. Extending that architecture to 32 bolometers requires an increase in the bandwidth of the SQUID electronics to 3 MHz. To achieve this increase in bandwidth, we use Digital Active Nulling (DAN) on the digital frequency multiplexing platform. In this paper, we present requirements and improvements on parasitic inductance and resistance of cryogenic wiring and capacitors used for modulating bolometers. These components are problematic above 1 MHz. We also show that our system is able to bias a bolometer in its superconducting transition at 3 MHz.

astro-ph.IM↗

arXiv2007

Conduction Effect of Thermal Radiation in a Metal Shield Pipe in a Cryostat for a Cryogenic Interferometric Gravitational Wave Detector

A large heat load caused by thermal radiation through a metal shield pipe was observed in a cooling test of a cryostat for a prototype of a cryogenic interferometric gravitational wave detector. The heat load was approximately 1000 times larger than the value calculated by the Stefan-Boltzmann law. We studied this phenomenon by simulation and experiment and found that it was caused by the conduction of thermal radiation in a metal shield pipe.

physics.ins-det↗