Experimental Efforts to Detect Gravitational Waves

Abstract

A remarkable design of LCGT was established by experimental efforts to detect gravitational waves in Japan including optional alternatives in design detail. The LCGT adopts an advanced technique regarded to be used in the third generation. We can reliably detect gravitational waves by LCGT and still have a chance to firstly detect it. * ) Earth GEO600 Germany-Britain Hannover German at RMIT Central Library on July 6, 2015 http://ptps.oxfordjournals.org/ Downloaded from 56 K. Kuroda et al.revised so as to consider technical developments and the experience obtained in a series of data-taking runs by TAMA. Remarkable feature of LCGTLCGT is designed to ultimately increase the sensitivity of a Fabry-Perot Michelson interferometer using existing technologies. Cryogenic mirrors are adopted for the main cavities of the interferometer to reduce thermal vibration noise. In place of synthetic silica, sapphire crystal has to be used for the mirror substrate. Since sapphire has much higher optical loss, 8) we have applied the technique of the resonant sideband extraction (RSE) 9) scheme with a relatively low-power recycling gain in order to reduce a problem arising from the higher optical loss inside the input mirror of Fabry-Perot cavity. The other item that characterizes LCGT is the suspension point interferometer (SPI), 10) which makes ease the design of both the mirror actuation system and the vibration isolation system in the cryostat, since it reduces the mechanical noise inevitably introduced by cooling heat links connected from the mirror suspension system to the inner radiation shield of the cryostat. The SPI is described in §7.The data collected by TAMA was usually contaminated by non-Gaussian noise, and many fake events resulted. 11) To reduce these fake events, two interferometers are installed in the same vacuum system, which is a change of the previous revised design. 12), 13) From the report of LIGO, Hanford, the cross talk of two interferometers in the same vacuum tube was not seriously large. Even if there is some correlation between the two interferometers in LCGT, the simulated rejection ratio about the known wave-form signal is practically high enough as described in §3. Therefore, the choice of two interferometers gives us profound benefit for reliable detection of gravitational waves.The optical design of LCGT is shown in Fig. 2. It is a power recycled Fabry-Perot Michelson interferometer with RSE method. The output of the laser source is fed through two stages of mode cleaners into the main interferometer. The optical features of LCGT are described in §5 in detail.The cryogenic mirror allows us to design the sensitivity of the interferometer, limited only by quantum noises: shot noise and pressure noise of the photon recoil force. If we can establish this quantum-limited sensitivity, the sensitivity of the observational band is altered only by the signal bandwidth and the optical power in the cavity. By optimizing these two parameters, we can increase the detectable distance of the gravitational wave e...

Probing nontensorial polarizations of stochastic gravitational-wave backgrounds with ground-based laser interferometers

“…However, the first detection of the GW has not been achieved yet. The development of interferometers of the next generation, such as AIGO [4], advanced LIGO [5], advanced VIRGO [6], and LCGT [7], is underway. In the coming decade, a direct detection of GWs will be made, and the GW experiments will be a key observational tool to obtain valuable information about astronomical objects and physics of the early universe.…”

Quantum noise of a Michelson-Sagnac interferometer with a translucent mechanical oscillator

“…The interferometric gravitational wave detectors in their first generation achieve a linear noise spectral density for the displacement measurement of as low as 10 −19 m/Hz 1/2 [1]. The gravitational wave detectors of the second generation [2,3,4] are designed to have a ten times better sensitivity. The sensitivity of these interferometers will be limited by quantum radiation pressure noise [5] at low audio-band Fourier frequencies and by photon shot noise [5] at higher frequencies.…”

Identification of gravitational-wave bursts in high noise using Padé filtering

“…Ground based GW interferometers (LIGO [1], Virgo [2], GEO600 [3] and TAMA300 [4]), in operation during the first decade of the century, have demonstrated the feasibility of the experiment. The second generation of LIGO/Virgo detectors (Advanced LIGO [5], Advanced Virgo [6]) will start collecting data in 2015, opening the era of the first detections, including tens of compact binary coalescences a year and maybe occasional supernovas.…”