Diffraction losses of a Fabry-Perot cavity with nonidentical non-spherical mirrors

Optical cavities with both optimized resonant conditions and high quality factors are important metrological tools. In particular, they are used for laser gravitational wave (GW) detectors. In order to have high cavity powers in GW detectors, it is necessary to suppress the parametric instability and to reduce the loss in the arm caused by point absorbers by damping the resonant conditions of harmful higher order optical modes (HOOM). This can be achieved effectively by using non spherical mirrors in symmetric Fabry-Perot (FP) cavities by increasing roundtrip losses of HOOMs [1, 2]. Fabry-Perot cavities in most of the GW detectors have non-identical mirrors to optimize clipping losses and reduce thermal noise by reducing the beam size on one side of the cavity facing to the beam splitter and recycling cavities. We here present a general method to design non spherical non-identical mirrors in non-symmetric FP cavities to damp HOOMs. The proposed design allows to the suppress the loss of the arm power caused by point absorbers on test masses.

兼具优化谐振条件与高品质因数的光学腔是重要的计量工具。尤其，它们被用于激光引力波（GW）探测器。为了在引力波探测器中获得高腔功率，需通过抑制有害高阶光学模式（HOOM）的谐振条件，来压制参数不稳定性并减少由点吸收体导致的臂部损耗。通过在对称法布里-珀罗（FP）腔中使用非球面镜以增加高阶光学模式的往返损耗，可有效实现这一目标[1,2]。大多数引力波探测器中的法布里-珀罗腔采用非相同反射镜，通过减小腔中面向分束器与回收腔一侧的光束尺寸，优化截断损耗并降低热噪声。本文提出一种在非对称FP腔中设计非球面非相同反射镜以抑制高阶光学模式的通用方法。该设计可抑制由测试质量块上的点吸收体导致的臂部功率损耗。