Advanced LIGO: Research on Mode Matching and Control Systems

将研究一种新的光学设计和一种改进的长度传感方案，以便按计划升级目前的LIGO探测器。在Advanced LIGO中使用的很高的激光功率会使反射镜变形，并降低干涉仪中各光腔之间的模式匹配。在新的光学设计中，输入光学链中的扩束器被移动到功率回收腔内。这使得在安装所有光学元件并在现场测量热变形之后，可以优化干涉仪内部各种光腔之间的模式匹配。然而，新布局的热模型是必要的，并将在未来几年进行优化设计。此外，目前用于高级LIGO的长度检测方案具有一定的局限性，因为它需要相当高的调制频率，但仍然产生高度耦合的检测矩阵。将在未来几年推出的修改后的长度传感方案将使用非谐波、低频调制信号来显著减少这些问题。激光干涉仪引力波天文台(LIGO)在华盛顿州汉福德和洛杉矶利文斯顿分别运行两个激光干涉仪和一个激光干涉仪，以探测来自天体物理源的引力波。目前的LIGO干涉仪将在几年内进行升级，以提高其灵敏度，以便更好地分辨波形和定位源。这项研究将开发优化先进LIGO探测器中各种光腔之间的空间模式匹配的技术。这将增加信号强度，降低对激光光束指向和强度波动等许多技术噪声源的要求。

A study of a new optical design and a modified length sensing scheme for the planned upgrade of the current LIGO detector will be performed. The very high laser power used in Advanced LIGO will deform the mirrors and degrade the mode matching between the various optical cavities in the interferometer. In the new optical design the beam expander in the input optics chain is moved inside the power recycling cavity. This makes it possible to optimize the mode matching between the various optical cavities inside the interferometer after all optical components are installed and the thermal deformations are measured on site. However, thermal modeling of the new layout is necessary and will be done over the next years to optimize this design. In addition, the current length sensing scheme for Advanced LIGO has some limitations because it requires rather high modulation frequencies but still generates a highly coupled sensing matrix. The modified length sensing scheme which will be derived over the next years will use non-harmonic, low-frequencymodulation signals to reduce these problems significantly. The Laser Interferometer Gravitational Wave Observatory (LIGO) operates two laser interferometer in Hanford, WA, and one in Livingston, LA, to detect gravitational waves from astrophysical sources. The current LIGO interferometers will have to be upgraded in a few years to improve thesensitivity to better resolve the waveforms and locate the sources. This research will develop technologies to optimize the spatial mode matching between the various optical cavities in the Advanced LIGO detector. This will increase the signal strength and reduce the requirements on many technical noise sources like laser beam pointing and intensity fluctuations.