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。     

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.     

太极计划激光指向调控方案介绍

空间引力波探测中为实现引力波信号科学测量,卫星发射到预定轨道后需首先完成百万公里级激光链路的构建。同时为保证引力波信号不会被激光指向噪声淹没,激光指向稳定性需达到nrad/((Hz)~(1/2))量级。为此需设计一套复杂而精密的激光指向调控方案。本文以太极计划为背景,详细阐述了可采用的指向调控方案。拟将整个过程将分为两个阶段,首先进行激光捕获过程,在该过程中,使用星敏感器(STR)与电荷耦合器件(CCD)作为辅助捕获探测器,将激光指向不确定区域控制到μrad量级。之后进行激光精密指向过程,利用差分波前敏感测角(DWS)技术对激光指向稳定性进行控制。根据太极计划要求,对各阶段捕获探测器提出了视场及精度要求,并论述了采用DWS技术实现精密指向的可行性。相关结论可为未来的验证实验奠定理论基础,对太极计划指向系统构建提供参考。     

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。     

引力波背景下的电磁波

本文首先介绍了激光干涉引力波探测实验原理教学的时空图方法,紧接着对引力波背景下一种具有简单然而非平庸时空轮廓的电磁场的波动方程进行了化简并求出了其解析解,最后利用所得解对激光干涉引力波探测实验中测地光子近似的有效性进行了定量的评估和分析。我们的结果对激光干涉引力波探测原理和弯曲时空中麦克斯韦方程组及电磁波理论的教学有积极的探讨价值。     

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。     

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。     

空间引力波望远镜远场相位噪声抑制方法

空间引力波望远镜的波像差与指向抖动耦合产生的远场相位噪声是引力波探测的主要噪声源。基于其产生的理论机制，建立了噪声耦合系数与望远镜像差间的函数关系，提出了控制特定像差的优化策略。结合望远镜设计实例验证了该方法对抑制远场相位噪声的效果，当波前质量水平为λ/20（λ=1064nm）时，优化后的噪声耦合系数优于0.11 pm/nrad，较优化前降低了一个数量级，远优于指标要求，所提方法极大地提升了望远镜的远场相位稳定性。     

激光本振红外光谱干涉成像及其艇载天文应用展望(特邀)

本文分析了红外干涉成像现状和难点,介绍了激光本振红外相干探测的原理,阐述了基于电子学的红外光谱细分和干涉成像原理,讨论了激光本振红外阵列探测器形式.激光本振和相干探测器的设置,可保证两个望远镜的红外信号相位的正确传递,在电子学实施窄带滤波形成的窄带红外信号有利于实现长基线干涉成像.在此基础上,类似微波综合孔径射电望远镜...     

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。     

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.     

Limitations of atom interferometry for gravitational wave observations in space

A paper published recently (Hogan et al. in Gen. Relativ. Gravit. 43:1953–2009, 2011) suggests the use of atom interferometry between satellites in Earth orbit to observe gravitational waves. The proposed altitude and satellite separation are about 1,000 and 30 km respectively. The difference in acceleration between clouds of ultracold atoms in atom interferometers near the two satellites would be detected by using laser beams between the interferometers. Because of the measurement path being very short compared with the million km or longer measurement path for a proposed laser interferometer gravitational wave antenna in space, the sensitivity to differential fluctuations in the laser phase as seen by the atoms in the two atom interferometers is very high. Problems introduced by this high sensitivity to spurious laser beam phase changes will be described in the first part of this paper. Then other limitations on the performance and on the suggested types of sources that could be observed will be discussed.     

Stabilized lasers for advanced gravitational wave detectors

Second‐generation interferometric gravitational wave detectors require high‐power lasers with approximately 200 W of output power in a linear polarized, single‐frequency, fundamental‐mode laser beam. Furthermore very high temporal and spatial stability is required. This paper discusses the design of a 200 W pre‐stabilized laser (PSL) system and the underlying concepts. The PSL requirements for advanced gravitational wave detectors as well as for the laser system are described. The laser stabilization scheme proposed for the Advanced LIGO gravitational wave detector and the so‐called diagnostic breadboard will serve as examples to explain the general laser stabilization concepts and the achieved performance and its limitations.     

Precision measurement with atom interferometry

Development of atom interferometry and its application in precision measurement are reviewed in this paper. The principle, features and the implementation of atom interferometers are introduced, the recent progress of precision measurement with atom interferometry, including determination of gravitational constant and fine structure constant, measurement of gravity, gravity gradient and rotation, test of weak equivalence principle, proposal of gravitational wave detection, and measurement of quadratic Zeeman shift are reviewed in detail. Determination of gravitational redshift, new definition of kilogram, and measurement of weak force with atom interferometry are also briefly introduced.     

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.     

Displacement- and timing-noise-free gravitational-wave detection

Motivated by a recently invented scheme of displacement-noise-free gravitational-wave detection, we demonstrate the existence of gravitational-wave detection schemes insusceptible to both displacement and timing (laser) noises and are thus realizable by shot-noise-limited laser interferometry. This is possible due to two reasons: first, gravitational waves and displacement disturbances contribute to light propagation times in different manners; second, for an N-detector system, the number of signal channels is of the order Omicron(N(2)), while the total number of timing- and displacement-noise channels is of the order Omicron(N).     

Astrophysics from data analysis of spherical gravitational wave detectors

The direct detection of gravitational waves will provide valuable astrophysical information about many celestial objects. Also, it will be an important test to general relativity and other theories of gravitation. The gravitational wave detector SCHENBERG has recently undergone its first test run. It is expected to have its first scientific run soon. In this work the data analysis system of this spherical, resonant mass detector is tested through the simulation of the detection of gravitational waves generated during the inspiralling phase of a binary system. It is shown from the simulated data that it is not necessary to have all six transducers operational in order to determine the source’s direction and the wave’s amplitudes.