Sources and technology for an atomic gravitational wave interferometric sensor

We study the use of atom interferometers as detectors for gravitational waves in the mHz–Hz frequency band, which is complementary to planned optical interferometers, such as laser interferometer gravitational wave observatories (LIGOs) and the Laser Interferometer Space Antenna (LISA). We describe an optimized atomic gravitational wave interferometric sensor (AGIS), whose sensitivity is proportional to the baseline length to power of 5/2, as opposed to the linear scaling of a more conservative design. Technical challenges are briefly discussed, as is a table-top demonstrator AGIS that is presently under construction at Berkeley. We study a range of potential sources of gravitational waves visible to AGIS, including galactic and extra-galactic binaries. Based on the predicted shot noise limited performance, AGIS should be capable of detecting type Ia supernovae precursors within 500 pc, up to 200 years beforehand. An optimized detector may be capable of detecting waves from RX J0806.3+1527.     

Physics of interferometric gravitational wave detectors

The Caltech-MIT joint LIGO project is operating three long-baseline interferometers (one of 2 km and two of 4 km) in order to unambiguously measure the infinitesimal displacements of isolated test masses which convey the signature of gravitational waves from astrophysical sources. An interferometric gravitational wave detector like LIGO is a complex, non-linear, coupled, dynamic system. This article summarizes various interesting design characteristics of these detectors and techniques that were implemented in order to reach and maintain its operating condition. Specifically, the following topics are discussed: (i) length sensing and control, (ii) alignment sensing and control and (iii) thermal lensing which changes the performance and operating point of the interferometer as the input power to LIGO is increased.     

低轨道轻质星载一体化空间光学遥感器的热设计

根据空间光学遥感器的轨道特点和任务需求,通过仿真分析对其进行了热设计。考虑近地空间环境的特殊性,选择防原子氧布作为多层隔热材料的面膜。为减小遥感器框架上安装的星上设备对遥感器温度的影响,设计了大热阻安装结构并使用了聚酰亚胺隔热垫。根据离轴三反光学遥感器及星载一体化卫星的结构特点,划分了主动加热区域,分配了加热功耗。由于遥感器对地观测频率低、工作功耗小、工作时间短,CCD焦面组件不设置散热面。根据遥感器的轨道参数和姿态,确定了3个典型工况并对其进行了仿真分析和热平衡试验。结果显示,遥感器本体温度为（18±4）℃、光学元件温度为（18±2）℃、CCD温度≤30℃,得到的仿真分析结果和试验数据验证了遥感器热设计的有效性。     

Nanohertz gravitational wave searches with interferometric pulsar timing experiments

We estimate the sensitivity to nano-Hertz gravitational waves of pulsar timing experiments in which two highly stable millisecond pulsars are tracked simultaneously with two neighboring radio telescopes that are referenced to the same timekeeping subsystem (i.e., "the clock"). By taking the difference of the two time-of-arrival residual data streams we can exactly cancel the clock noise in the combined data set, thereby enhancing the sensitivity to gravitational waves. We estimate that, in the band (10(-9)-10(-8)) Hz, this "interferometric" pulsar timing technique can potentially improve the sensitivity to gravitational radiation by almost 2 orders of magnitude over that of single-telescopes. Interferometric pulsar timing experiments could be performed with neighboring pairs of antennas of the NASA's Deep Space Network and the forthcoming large arraying projects.     

Arm cavity resonant sideband control for laser interferometric gravitational wave detectors

We present a new optical control scheme for a laser interferometric gravitational wave detector that has a high degree of tolerance to interferometer spatial distortions and noise on the input light. The scheme involves resonating the rf sidebands in an interferometer arm cavity.     

Detecting gravitational wave with an interferometric seismometer array on lunar nearside

Our Moon is by far the easiest natural, extraterrestrial celestial object for us to reach, and many space agencies, in particular the China National Space Administration, have publicized plans for manned missions there. Such high-profile projects must yield commensurate scientific outputs to justify their cost to the taxpayers. An important criterion for the selection of candidate experiments is the extent to which the Moon plays an integral and irreplaceable role, as opposed to offering only ma...     

Reduction of thermal fluctuations in a cryogenic laser interferometric gravitational wave detector

The thermal fluctuation of mirror surfaces is the fundamental limitation for interferometric gravitational wave (GW) detectors. Here, we experimentally demonstrate for the first time a reduction in a mirror's thermal fluctuation in a GW detector with sapphire mirrors from the Cryogenic Laser Interferometer Observatory at 17 and 18 K. The detector sensitivity, which was limited by the mirror's thermal fluctuation at room temperature, was improved in the frequency range of 90 to 240 Hz by cooling the mirrors. The improved sensitivity reached a maximum of 2.2×10(-19) m/√Hz at 165 Hz.     

O atom etching of graphite in low earth orbit

Samples of highly ordered pyrolytic graphite were placed aboard the space shuttle Atlantis (mission STS46) and exposed to the atmosphere present in low earth orbit to observe the effects of chemical etching by atomic oxygen on carbon-based materials. During the 43 h exposure, approximately 2.25 μm of graphite were removed from the sample, which corresponds to an etch yield of one C atom for every eight incident O atoms. The topography of the etched samples was analyzed quantitatively within the framework of scaling theory, and the experimental data agree with the static scaling behavior predicted for a model in which surface diffusion and reaction at step edges dominates the etching mechanism.     

Thin walled Nb tubes for suspending test masses in interferometric gravitational wave detectors

In a previous Letter, we have shown that the use of orthogonal ribbons could provide a better mirror suspension technique in interferometric gravitational wave antennas. One of the key improvements presented by the orthogonal ribbon is the reduction in the number of violin string modes in the direction of the laser. We have considered more elaborate geometries in recent simulations and obtained a suspension that provides further reduction in the number of violin string modes in the direction of the laser, as well as in the direction orthogonal to the laser. This thin walled niobium tube suspension exhibits a reduction in the number of violin modes to 5 in each direction up to a frequency of 5 kHz. Furthermore, the violin mode thermal noise peaks can be reduced in amplitude by 30 dB.     

Estimate of the cosmic ray background in an interferometric antenna for gravitational wave detection

The effect of the cosmic ray interaction in the masses of an interferometric antenna for gravitational wave (GW) detection is evaluated. In a 3 km antenna this background, mainly due to muons gives a limit, for 1 ms GW pulses, of h∼8.5×10^-23 with a frequency of 2×10^-1 events/year and 8.5×10^-26 with 4.1×10^-6 events/year. For GW having frequency>10 Hz the sensitivity limit is h∼1.7×10^-31. This background seems to allow unshielded operation of the interferometer test masses.     

An off-axis Hartmann sensor for the measurement of absorption-induced wavefront distortion in advanced gravitational wave interferometers

We describe a novel off-axis Hartmann wavefront sensor, developed for the measurement of wavefront distortions induced in the mirrors (test masses) of advanced gravitational wave interferometers by residual absorption of the circulating laser power.     

A reflection interferometer with transmission-like characteristics as an element of interferometric gravitational wave detectors

It is proposed to replace the Fabry-Perot interferometers incorporated into the combined Fabry-Perot-Michelson interferometer (FPMI) by transmission-like reflection interferometers (TRIs), creating bright (transmission-like) interference fringes in the reflected light. TRIs employ asymmetric metal-dielectric mirrors with a “matching” absorbing layer. The calculations show that the shot noise-limited sensitivity of an FPMI with TRIs is nearly as high as that of a conventional FPMI (for the same quality of dielectric coatings). In the presence of scattered light or when the laser and interferometer modes are not coupled well enough, the new version of the FPMI offers considerable advantages due to the mode-filtering properties of a TRI.     

Estimation of neutron and other radiation exposure components in low earth orbit

The interaction of high-energy space radiation with spacecraft materials generates a host of secondary particles, some, such as neutrons, are more biologically damaging and penetrating than the original primary particles. Before committing astronauts to long term exposure in such high radiation environments, a quantitative understanding of the exposure and estimates of the associated risks are required. Energetic neutrons are traditionally difficult to measure due to their neutral charge. Measurement methods have been limited by mass and weight requirements in space to nuclear emulsion, activation foils, a limited number of Bonner spheres, and TEPCs. Such measurements have had limited success in quantifying the neutron component relative to the charged components. We will show that a combination of computational models and experimental measurements can be used as a quantitative tool to evaluate the radiation environment within the Shuttle, including neutrons. Comparisons with space measurements are made with special emphasis on neutron sensitive and insensitive devices.     

Behavior of a test body in a plane gravitational (gravity) wave

The motion of a test particle in a plane gravity wave characterized by the metricds ²=e ^y c ² dt ² –e ^y dx ² –dy ² –dz ². is considered. It is shown that, in the case of velocities smaller than the velocity of light, when and vary harmonically, the test particle will execute harmonic oscillations along the x, y, and z axes.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 112–115, January, 1975.     

Investigation of Brownian coating noise in laser interferometric gravitational antennas

We report the results of a detailed study of the Brownian noise of an interferometric coating, which is the principal factor that limits the sensitivity of laser gravitational antennas. It is established that the noise level is lower than previously anticipated due to the influence of interference that takes place inside the coating. Optimizing a coating with the goal of decreasing the Brownian noise is attempted.     

低轨空间目标地基偏振成像系统偏振定标方法

针对地基大口径望远镜的机上自适应光学系统构建的低轨空间目标偏振成像系统,提出一种基于非偏振标准星和机上起偏装置的宽带偏振定标方法。该方法以非偏振标准星作为光源,并在望远镜系统的一次像面处加入起偏装置对入射光的偏振态进行调制,再结合基于非线性最小二乘拟合的偏振定标方法分两步对整个偏振成像系统进行宽带偏振定标。为验证该偏振定标方法的效果,利用Matlab软件基于相干矩阵和偏振追迹构建了相应的模型进行仿真分析,仿真结果表明该偏振定标方法可以有效减小望远镜系统偏振效应对偏振探测准确性的影响,并且偏振定标元件的初始角度误差在±5°范围内时对偏振定标准确性的影响极小。