Advanced LIGO: Research on Mode Matching and Control Systems

将进行一项新的光学设计和改进的长度传感方案的研究，以用于当前LIGO探测器的计划升级。在高级LIGO中使用的高功率激光会使反射镜变形，并降低干涉仪中各个光学腔之间的模式匹配。在新的光学设计中，输入光链中的光束扩展器被移动到功率回收腔内。这使得在安装完所有光学元件并现场测量热变形后，可以优化干涉仪内部各光腔之间的模式匹配。然而，新布局的热建模是必要的，并将在未来几年内完成，以优化该设计。此外，目前用于高级LIGO的长度传感方案存在一定的局限性，因为它需要较高的调制频率，但仍然产生高耦合的传感矩阵。修改后的长度传感方案将在未来几年推出，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）在华盛顿州的汉福德（Hanford）和洛杉矶的利文斯顿（Livingston）分别运行两个激光干涉仪，以探测来自天体物理源的引力波。目前的LIGO干涉仪必须在几年内升级，以提高灵敏度，更好地分辨波形并定位光源。本研究将开发优化先进LIGO探测器各光学腔间空间模式匹配的技术。这将增加信号强度，并减少对许多技术噪声源的要求，如激光束指向和强度波动。

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.