Converting the signal-recycling cavity into an unstable optomechanical filter to enhance the detection bandwidth of gravitational-wave detectors
Converting the signal-recycling cavity into an unstable optomechanical filter to enhance the detection bandwidth of gravitational-wave detectors
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DOI：
10.1103/physrevd.99.102001
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发表时间：
2019-05-14
影响因子：
5
通讯作者：
Miao, Haixing
中科院分区：
文献类型：
--
作者：
Bentley, Joe;Jones, Philip;Miao, Haixing
目前和未来的干涉引力波探测器主要受到高频散粒噪声的限制。通过引入臂腔和信号回收可以降低散粒噪声，但是在峰值灵敏度和带宽之间存在折衷。这来自于信号边带在臂腔内传播时的累积相位。一种想法是通过引入不稳定的光学机械滤波器来消除这样的相位。在[Phys. Rev. Lett. 115，211104（2015）]需要在外部耦合到主干涉仪的附加光机械滤波器。在这里，我们考虑了一个简化的设计，通过使用一个反射镜作为高频机械振荡器，并引入一个额外的泵浦激光器，将信号回收腔本身转换为不稳定的滤波器。然而，这种新设计的带宽的增强小于给定相同的光学参数集的原始设计。峰值灵敏度改善因子取决于臂长、信号再循环腔长和最终检测器带宽。对于4 km的干涉仪，如果最终检测器带宽约为2 kHz，使用20 m的信号回收腔，除了通过压缩光注入引入的改善之外，散粒噪声还可以降低10分贝。我们还发现，机械振荡器的热噪声在低频相对于真空噪声被放大，而在高频具有平坦的频谱。
Current and future interferometeric gravitational-wave detectors are limited predominantly by shot noise at high frequencies. Shot noise is reduced by introducing arm cavities and signal recycling, however, there exists a trade-off between the peak sensitivity and bandwidth. This comes from the accumulated phase of signal sidebands when propagating inside the arm cavities. One idea is to cancel such a phase by introducing an unstable optomechanical filter. The original design proposed in [Phys. Rev. Lett. 115, 211104 (2015)] requires an additional optomechanical filter coupled externally to the main interferometer. Here we consider a simplified design that converts the signal-recycling cavity itself into the unstable filter by using one mirror as a high-frequency mechanical oscillator and introducing an additional pump laser. However, the enhancement in bandwidth of this new design is less than the original design given the same set of optical parameters. The peak sensitivity improvement factor depends on the arm length, the signal-recycling cavity length, and the final detector bandwidth. For a 4 km interferometer, if the final detector bandwidth is around 2 kHz, with a 20 m signal-recycling cavity, the shot noise can be reduced by 10 decibels, in addition to the improvement introduced by squeezed light injection. We also find that the thermal noise of the mechanical oscillator is amplified at low frequencies relative to the vacuum noise, while having a flat spectrum at high frequencies.