Noises In Relic Gravitational Wave Detecting Experiment

The detection of gravitational wave (GW) is a validation of the general relativity, and is also a new method of observing the universe. Relic GW occurred during the earlier period of the universe evolvement, it is some kind of random background which is caused by the amplificatory zero point fluctuation of the universe. It also takes along important information of the evolvement of the earlier universe. Through the detection, we could know more about the earlier universe.Though there are several detecting schemes (LIGO, VIRGO, GEO 600, TAMA 300) being actualized, most of the detecting frequencies distribute in the low frequency district (10-4-104Hz). The frequencies of the relic GW could reach up to 1010Hz, out of the low frequency district, it's a kind of high frequency GW. Hence, a new detecting scheme for this kind of GW is needed. Prof. Fang-Yu Li etc. developed a detecting scheme. In this scheme, a beam of high energy microwave (Gaussian Beam) passes through a cylindrical cavity along the central axis. The interaction between the Gaussian beam and the probably relic GW in the cavity will change the propagating directions of some photons. Those deflexed photons will pass through a rectangular channels upright to the central axis of the cavity and will be detected by a microwave detector at the bottom of the channels.The efficiency of a scheme of signal detection is depended on its SNR. GW's are very weak signals, so detecting GW's requires very weak noises in both the equipment and the environment. So it's important to analyze the noises for the scheme. In this paper, we will analyze three basic kinds of noises unavoidable in Fang-Yu Li's scheme. They are the fluctuation of the background thermal radiation of the cavity, the scattering of Gaussian Beam in the cavity, and the thermal noises in the microwave radiometers.