Innovative Quantum Noise reduction strategies for GW detectors

在2022财年，为了提高滤腔的稳定性，采取了几项措施。自2021财年以来，对滤光腔长度、对准和入射光束指向自由度的双色控制进行了研究，最终确定了使用双色控制。这是理解红外线锁和绿锁之间关系的关键一步。发表了一篇关于《物理评论D》的论文。在这种控制下，滤光腔失谐改善了6倍，使该参数符合KAGRA的实施要求。此外，文中提出的方案也被意大利-法国引力波探测器Virgo正式采用。还实现了提高滤光腔稳定性的另一步，即通过本课题组在2019年理论上提出的相干控制边带方案，实现了滤光腔锁定的实验演示。这一演示的结果也发表在《物理评论D》上。此外，还执行了几个步骤来减少光学损耗的影响。特别是对新型低损耗法拉第光隔离器进行了表征，并实现了新型低损耗光学参变振荡器。新的低损耗组件将允许更好地描述散射损耗，这反过来将导致更好地理解抛光规范在滤光腔系统中的作用。

In FY2022 several steps were taken in order to improve the stability of the filter cavity. The use of a bichromatic control for the filter cavity length, alignment and incident beam pointing degree of freedoms was finalized after being studied since FY2021. This was a crucial step in understanding the relationship between infrared lock and green lock. A paper on Physical Review D was published on it. With this control, a factor of 6 improvement on the filter cavity detuning was achieved, bringing this parameter within the requirement for implementation in KAGRA. In addition, the scheme proposed in the paper was officially adopted also by the Italian-French gravitational wave detector named Virgo. Another step done to improve the stability of the filter cavity was also achieved which was the experimental demonstration of the lock of the filter cavity via the coherent control sidebands scheme proposed theoretically by our group in 2019. The results of this demonstration have also been published in Physical Review D.In addition, several steps have been performed to reduce the impact of optical losses. In particular, the new low losses Faraday isolator has been characterized and the new low loss Optical Parametric Oscillator has been realized and characterized. The new low losses component will allow for a better characterization of scattering losses which will in turn lead to better understanding the role of polishing specs in the filter cavity system.