Advanced LIGO: Research on Mode Matching and Control Systems

一个新的光学设计和修改长度传感计划的升级目前的LIGO探测器的研究将进行。Advanced LIGO中使用的非常高的激光功率会使反射镜变形，并降低干涉仪中各种光学腔之间的模式匹配。在新的光学设计中，输入光学链中的扩束器在功率回收腔内移动。这使得在安装所有光学部件并现场测量热变形之后，可以优化干涉仪内部的各种光学腔之间的模式匹配。然而，新布局的热建模是必要的，并将在未来几年内完成，以优化这一设计。此外，Advanced LIGO的电流长度感测方案具有一些局限性，因为它需要相当高的调制频率，但仍然生成高度耦合的感测矩阵。修改后的长度传感方案将在未来几年内推出，将使用非谐波，低频调制信号，以减少这些问题显着。 激光干涉引力波天文台（LIGO）在华盛顿州的汉福德和洛杉矶的利文斯顿分别运行两台激光干涉仪，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，从而更好地解析波形并定位源。这项研究将开发技术，以优化先进LIGO探测器中各种光学腔之间的空间模式匹配。这将增加信号强度并降低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.