通向天基引力波探测器

正来自LISA探路者任务的初步结果表明,对于处于自由落体状态的两个测试立方体,它们之间的相对加速的噪声很小,满足天基引力波探测的要求。2016年2月,激光干涉引力波天文台(LIGO)探测到由两个黑洞合并引发的引力波。这一结果的公布使很多物理和天文学领域的科学家感到震惊和兴奋。当所有的眼光转向LIGO时,LISA探路者(LPF)正静悄悄但信心十足地为引力波天文学的下一场革命铺平道路。LPF是激光干涉空     

空间引力波探测中的绝对距离测量及通信技术

空间引力波探测任务中,由于干涉臂臂长的巨大差异,激光频率不稳定噪声成为系统最大的噪声源之一。需采用Pound-Drever-Hall锁腔、锁臂和TDI(Time Delay Interferometer)技术三级联合,将此噪声压制到10~(-6)Hz~(1/2)量级,才能使得频率噪声低于散粒噪声。而实现TDI技术需要准确测量卫星间的绝对距离和星间通信。本文以空间引力波探测中的绝对距离测量和通信技术为背景,详细阐述此项技术的实现原理和方法。拟通过EOM(Electro-Optic Modulator)将测距伪随机码和通信码调制至主激光相位中,再传输至远端航天器。在远端航天器通过锁相环和延迟环组成的解调系统计算伪随机码的时间延迟,进而解析出卫星间的绝对距离和通信信息。相关结论可为未来的验证实验奠定理论和技术基础,同时为我国未来空间引力波探测的相关技术发展提供一定参考。     

在所有频段感受挤压

正两个小组展示了频率依赖的量子压缩,这项技术可以使引力波探测器的灵敏度加倍。引力波天文台最近开始着手"挤压"探测器中的激光。这项技术降低了噪声,提高了灵敏度,但仅仅是在一个有限的频率范围内。现在两个小组已经展示了一个降低噪声的新方法,它覆盖一个宽波段的引力波频率范围。这种量子压缩技术,当它与其他升级手段一起部署时,将使引力波天文台的探测灵敏度加倍。     

用零输出的设备探测引力波

理论估计传到地球上的引力波非常弱,激光干涉引力波探测器被设计用来探测引力波,在没有引力波传来时,激光干涉引力波探测器应该是零输出。为达到这样的目的,必须和众多的噪声作斗争。     

地基引力波探测激光干涉仪的真空残余气体噪声分析

引力波是时空弯曲产生的涟漪波动.引力波探测对促进人类认识自然和科学技术进步均具有深远意义.由于引力波信号非常微弱,地基引力波探测器需要超高真空环境来保证激光干涉仪的稳定运行.本文阐述了残余气体噪声对地基引力波探测装置灵敏度的影响,并从第三代地基引力波探测原型机和全尺寸装置的真空系统设计出发,通过理论分析和模拟,给出真空系统压强、环境温度、残余气体质量和种类、测试质量的曲率半径等因素对引力波探测灵敏度的影响.这为引力波探测原型机和全尺寸装置的真空系统设计和建设提供了重要的理论依据.     

面向空间引力波探测的低噪声稳频激光器

基于未来卫星间激光干涉任务的需求,介绍了一种基于迈克耳孙光纤干涉仪稳频的1064 nm激光稳频系统,该系统采用全光纤器件,结构紧凑、体积小、可靠性强。通过拍频测试,得到该系统的频率噪声在30 mHz～1 Hz范围内小于30 Hz/Hz1/2,频率稳定度在积分时间为1 s和1000 s时分别为1.2×10-14和3×10-13。该系统的性能满足LISA任务对稳频激光的需求,有望应用于未来的空间引力波探测任务。     

引力波与引力波探测:一个全新的空间信息通道

简述了引力波探测的历史,介绍了对质量谐振探测器、地面激光干涉引力波探测器、空间激光干涉引力波探测器,以及引力波在宇宙微波背景上极化效应的相关探测方案,评述了微波频带的高频引力波探测方案.     

激光干涉引力波探测器——人类的宇宙助听器

爱因斯坦预言引力波100周年之际,人类首次直接探测到引力波信号。文章简单介绍了这次的主角——高新激光干涉引力波天文台(advanced LIGO)的光学与激光部分技术。激光干涉引力波探测器,本质上是一个迈克尔孙干涉仪。原初的迈克尔孙干涉仪也曾在否定以太理论、促使相对论创立的过程中起关键作用。而基于爱因斯坦受激发射理论发展起来的激光技术也在引力波探测中立下汗马功劳。出于协同测量与定位以及扩展引力波探测频段等方面的考虑,除LIGO之外,还有多个地面和空间激光干涉引力波探测器在建或在研。可以预计,当前只是引力波探测技术与引力波天文学发展的开端。     

用于引力波关键技术验证的近地低成本商业卫星设计

地面引力波探测由于受到地表振动、重力梯度等噪声以及试验尺度的限制,探测频段被限制在10Hz以上,而对于更大特征质量和尺度的波源,探测频段主要在中低频段(0. 1 mHz～1 Hz)。因此,为避免地面干扰,需要在空间进行探测。由于引力波信号微弱,探测精度极高,针对空间引力波探测,国际上提出了以LISA为代表的空间引力波探测计划,国内中国科学院也提出了太极计划。然而,国内外的引力波探测卫星计划,对卫星的技术指标、设计复杂性和成本均提出了极高要求,短期之内难以实现。针对这一现实情况,本文参考LISA pathfinder的设计思路,设计一颗近地低成本商业卫星,针对引力波探测关键技术的验证需求,进行卫星任务需求分析及结构、热控、姿态控制等关键技术分析,提出商业化的低成本技术验证初步设想,希望能对空间引力波探测卫星总体设计提供一定借鉴。     

大质量镜面感知光子力的起伏

LIGO和Virgo在实验中测量到了未曾观察过的作用在宏观尺度上的量子效应。要察觉引力波的存在,Virgo(欧洲室女座天文台)和LIGO(美国激光干涉引力波天文台)需要能检测到激光干涉臂的微小改变——小到只有质子直径的万分之一。研究人员已经通过有效降低"技术"噪声(比如来自地震的扰动和电子设备的干扰),实现了如此灵敏的探测。此时探测器的噪声已经接近量子散粒噪声这个无法避免的基本限制。     

EOM sideband phase characteristics for the spaceborne gravitational wave detector LISA

The Laser Interferometer Space Antenna (LISA) is a joint ESA/NASA mission proposed to observe gravitational waves. One important noise source in the LISA phase measurement will be on-board reference oscillators. An inter-spacecraft clock tone transfer chain will be necessary to remove this non-negligible phase noise in post processing. One of the primary components of this chain are electro-optic modulators (EOMs). At modulation frequencies of 2 GHz, we characterise the excess phase noise of a fibre-coupled integrated EOM in the LISA measurement band (0.1 mHz to 1 Hz). The upper phase noise limit was found to be almost an order of magnitude better than required by the LISA mission. In addition, the EOM’s phase dependence on temperature and optical power was determined. The measured coefficients are within a few milliradians per kelvin and per watt respectively and thereby negligible with the expected on-board temperature and laser power stability.     

Fully Data-Driven Time-Delay Interferometry with Time-Varying Delays

Raw space-based gravitational-wave data like laser interferometer space antenna's (LISA) phase measurements are dominated by laser frequency noise. The standard technique to make this data usable for gravitational-wave detection is time-delay interferometry (TDI), which cancels laser noise terms by forming suitable combinations of delayed measurements. To do so, TDI relies on inter-spacecraft distances and on how laser noise enters the interferometric data. The basic concepts of an alternative approach which does not rely on independent knowledge of temporal correlations in the dominant noise recently introduced. Instead, this automated principal component interferometry (aPCI) approach only assumes that one can produce some linear combinations of the temporally nearby regularly spaced phase measurements, which cancel the laser noise. Then the data is let to reveal those combinations, thus providing a set of laser-noise-free data channels. The authors' previous approach relies on the simplifying additional assumption that the filters which lead to the laser-noise-free data streams are time-independent. In LISA, however, these filters will vary as the constellation armlengths evolve. Here, a generalization of the basic aPCI concept compatible with data dominated by a still unmodeled but slowly varying dominant noise covariance is discussed. Despite its independence on any model, aPCI successfully mitigates laser frequency noise below the other noises' level, and its sensitivity to gravitational waves is the same as the state-of-the-art second-generation TDI, up to a 2% error.     

Achieving geodetic motion for LISA test masses: ground testing results

The low-frequency resolution of space-based gravitational wave observatories such as LISA (Laser Interferometry Space Antenna) hinges on the orbital purity of a free-falling reference test mass inside a satellite shield. We present here a torsion pendulum study of the forces that will disturb an orbiting test mass inside a LISA capacitive position sensor. The pendulum, with a measured torque noise floor below 10 fN m/square root of Hz from 0.6 to 10 mHz, has allowed placement of an upper limit on sensor force noise contributions, measurement of the sensor electrostatic stiffness at the 5% level, and detection and compensation of stray dc electrostatic biases at the millivolt level.     

空间引力波探测计划-LISA系统设计要点

为了验证广义相对论,世界各国竞相开展了空间引力波探测方面的研究。本文以欧洲空间引力波探测LISA(Laser Interferometer Space Antenna)计划为例,根据基线设计,对LISA系统有效载荷及主要组件的设计进行了分析和阐述。LISA主要探测和研究低频引力波辐射,其工作频段为10^-3~1 Hz,工作距离为5×10⁶ km,预计能探测到双致密星系统以及星系合并引起的超大质量并合等波源,测距精度达到pm量级。以上研究希望能对我国未来的空间引力波探测计划有一定启示。     

Temporal extent of surface potentials between closely spaced metals

Variations in the electrostatic surface potential between the proof mass and electrode housing in the space-based gravitational wave mission Laser Interferometer Space Antenna (LISA) is one of the largest contributors of noise at frequencies below a few mHz. Torsion balances provide an ideal test bed for investigating these effects in conditions emulative of LISA. Our apparatus consists of a Au coated Cu plate brought near a Au coated Si plate pendulum suspended from a thin W wire. We have measured a white noise level of 30 microV/sqrt Hz above approximately 0.1 mHz, rising at lower frequencies, for the surface potential variations between these two closely spaced metals.     

Atomic Interferometric Gravitational-Wave Space Observatory(AIGSO)

We propose a space-borne gravitational-wave detection scheme, called atom interferometric gravitationalwave space observatory(AIGSO). It is motivated by the progress in the atomic matter-wave interferometry, which solely utilizes the standing light waves to split, deflect and recombine the atomic beam. Our scheme consists of three drag-free satellites orbiting the Earth. The phase shift of AIGSO is dominated by the Sagnac effect of gravitational-waves, which is proportional to the area enclosed by the a√tom interferometer, the frequency and amplitude of gravitational-waves.The scheme has a strain sensitivity 10~(-20)/Hz~(1/2) in the 100 mHz–10 Hz frequency range, which fills in the detection gap between space-based and ground-based laser interferometric detectors. Thus, our proposed AIGSO can be a good complementary detection scheme to the space-borne laser interferometric schemes, such as LISA. Considering the current status of relevant technology readiness, we expect our AIGSO to be a promising candidate for the future space-based gravitational-wave detection plan.     

大倍率离轴无焦四反光学系统设计

空间引力波探测任务采用的是外差法激光干涉测量技术,其对系统的噪声和精度要求极为苛刻。望远镜是引力波探测天文台的重要组成部分,起到激光信号收发的作用,其光学系统应具备大倍率、高像质、杂光抑制能力强,波前误差一致性好的特点。针对上述要求,对大倍率离轴四反无焦光学系统进行了设计和优化。基于初级像差理论阐述了初始结构的求解方法。系统具有中间像面和可用的实出瞳,便于杂光抑制和与后端科学干涉仪的承接。优化过程中,建立了波前一致性优化函数,通过优化设计,系统入瞳直径为200 mm,放大倍率为40倍,科学视场为±8μrad,波前误差RMS值优于0.005λ,PV值优于0.023λ(λ=1064 nm),波前一致性残差RMS值优于0.0008λ(λ=1064 nm),在捕获视场±200μrad内的成像质量均接近衍射极限,并对系统公差进行了分析,满足引力波探测的应用需求。     

Orbit optimization for ASTROD-GW and its time delay interferometry with two arms using CGC ephemeris

Astrodynamical space test of relativity using optical devices optimized for gravitation wave detection (ASTROD- GW) is an optimization of ASTROD to focus on the goal of detection of gravitation waves. The detection sensitivity is shifted 52 times toward larger wavelength compared with that of laser interferometer space antenna (LISA). The mission orbits of the three spacecrafts forming a nearly equilateral triangular array are chosen to be near the Sun-Earth Lagrange points L3, L4, and L5. The three spacecrafts range interferometrically with one another with an arm length of about 260 million kilometers. In order to attain the required sensitivity for ASTROD-GW, laser frequency noise must be suppressed to below the secondary noises such as the optical path noise, acceleration noise, etc. For suppressing laser frequency noise, we need to use time delay interferometry (TDI) to match the two different optical paths (times of travel). Since planets and other solar-system bodies perturb the orbits of ASTROD-GW spacecraft and affect the TDI, we simulate the time delay numerically using CGC 2.7 (here, CGC stands for center for gravitation and cosmology) ephemeris framework. To conform to the ASTROD-GW planning, we work out a set of 20-year optimized mission orbits of ASTROD-GW spacecraft starting at June 21, 2028, and calculate the differences in optical path in the first and second generation TDIs separately for one-detector case. In our optimized mission orbits of 20 years, changes of arm lengths are less than 0.0003 AU; the relative Doppler velocities are all less than 3m/s. All the second generation TDI for one-detector case satisfies the ASTROD-GW requirement.     

Gravitational wave detection by laser interferometry – on earth and in space

The space project LISA is approved by ESA as a cornerstone mission in the field of ‘fundamental physics’, sharing its goal and principle of operation with the ground-based interferometers currently under construction: the detection and measurement of gravitational waves by laser interferometry. Ground and space detection differ in their frequency ranges, and thus the detectable sources. At low frequencies, ground-based detection is limited by seismic noise, and yet more fundamentally by ‘gravity gradient noise’, thus covering the range from a few Hz to a few kHz. On five sites worldwide, detectors of armlengths from 0.3 to 4 km are being built, two of them in Europe (GEO and VIRGO). They will progressively be put in operation between 2001 and 2003. Future improved versions are being planned, with data not until 2008, i.e. near the launch of the space project LISA. It is only in space that detection of signals below, say, 1 Hz is possible, opening a wide window to a different class of interesting sources of gravitational waves. The project LISA consists of three spacecraft in heliocentric orbits, forming a triangle of 5 million km sides.     

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.