Development of Narrow-band Laser Interferometer Gravitational Wave Antenna

目前正在进行的几个项目旨在利用激光干涉仪探测引力波：日本的TAMA项目、美国的LIGO项目、法国-意大利的VIRGO项目和德国-英国的GEO项目。几年后很有可能探测到引力波。然而，为了建立引力波天文学，需要进一步提高天线的灵敏度。共振边带提取（RSE）是在有限频段内提高干涉仪灵敏度的先进技术之一。在这个项目中，我们对RSE干涉仪的性能进行了基础研究。RSE干涉仪需要在常规功率回收法布里-珀罗-迈克尔逊干涉仪的检测口放置一个额外的反射镜。这种信号提取镜使从臂腔中提取引力波信号成为可能，否则这些信号将被抵消。与传统干涉仪相比，RSE干涉仪的优点是回收腔内的激光功率较低，避免了由于反射镜的热透镜效应而导致的灵敏度下降。此外，RSE干涉仪可以在有限的频带内以更好的灵敏度操作，只需将信号提取镜替换为光波长的一小部分。迄今为止，在RSE干涉仪上进行过几次基础实验，但都是在空气中进行的桌面实验，并且都采用了多调制方案进行信号提取。由于RSE干涉仪对臂腔的精细度要求极高，因此反射镜的反射率极高，因此不建议在空气中操作干涉仪，因为空气中反射镜可能会退化。此外，桌面实验使用固定在桌子上的镜子，这与真正的引力波天线中悬挂的镜子有很大不同。此外，多调制方案使干涉仪的控制更加复杂。因此，在本研究中，我们使用小型悬挂系统在真空系统中进行实验，从而使环境更好，更逼真。我们还发明了一种单调制的信号提取方法，保证了控制系统的简单性。去年，我们终于在世界上首次成功地在真空悬挂镜系统中使用单调制方法操作了RSE干涉仪。然后，我们找到了一种更好的信号提取方法，使用三次谐波解调保持单一调制方案。我们从理论上分析了这种新方法，并通过仿真发现，该方法在不失去系统简洁性的情况下，效果更好。我们计划明年用实验来验证这个新方案。去年，我们终于在世界上首次成功地在真空悬挂镜系统中使用单调制方法操作了RSE干涉仪。然后，我们找到了一种更好的信号提取方法，使用三次谐波解调保持单一调制方案。对该方法进行了理论分析，仿真结果表明，该方法在保持系统简洁性的前提下，工作效果更好。我们计划明年用实验来验证这个新方案。少

There are several projects going on which aim at gravitational wave detection using laser interferometers : the Japanese TAMA project, the American LIGO project, the French-Italian VIRGO project, and the German-British GEO project. It is quite possible that gravitational waves could be detected in several years. However, it is necessary to improve the sensitivity of the antennas further in order to establish the gravitational wave astronomy. The resonant sideband extraction (RSE) is one of the advanced technologies which could improve the sensitivity of the interferometer in a limited frequency band. In this program we performed a basic research to investigate the performance of the RSE interferometer.The RSE interferometer requires an additional mirror placed at the detection port of the conventional power-recycled Fabry-Perot Michelson interferometer. This signal extraction mirror makes it possible to extract the gravitational wave signal from the arm cavity, which would be cancelled … More out otherwise. The RSE interferometer has an advantage that the laser power in the recycling cavity is lower compared with the conventional interferometer, which could avoid the degradation of sensitivity due to the heating lens effect of the mirrors. Moreover, the RSE interferometer can be operated with better sensitivity in a limited frequency band by simply displacing the signal extraction mirror by a fraction of the wavelength of the light.There has been several basic experiments on the RSE interferometer so far, but they were all performed as table-top experiments in the air, as well as they were all using multi-modulation schemes for signal extraction. Since the RSE interferometer requires an extremely high finesse of the arm cavity, thus, extremely high reflectivty of the mirrors, it is not preferable to operate the interferometer in the air because of possible degradation of the mirrors in the air. Also the table-top experiment uses mirrors fixed to the table, which are very different from the suspended mirrors in a real gravitational wave antenna. Moreover the multi-modulation scheme makes the interferometer control even more complicated.Therefore in this research, we performed the experiment in the vacuum system using a small suspension system, which made it possible to have a better and more realistic environment. Also we invented a single modulation method for signal extraction, which ensures the simplicity of the control system. In the last year we finally succeeded in operating the RSE interferometer using the single modulation method in a vacuum system using suspended mirrors for the first time in the wotld. After that we found a better way for signal extraction using the third harmonic demodulation maintaining the single modulation scheme. We analyzed this new method theoretically and using the simulation we found that the method would work even better without losing the simplicity of tlte system. We plan to verify this new scheme by experiment next year.In the last year we finally succeeded in operating the RSE interferometer using the single modulation method in a vacuum system using suspended mirrors for the first time in the wotld. After that we found a better way for signal extraction using the third harmonic demodulation maintaining the single modulation scheme. We analyzed this new method theoretically and using the simulation we found that the method would work even better without losing the simplicity of the system. We plan to verify this new scheme by experiment next year. Less