Most second-generation gravitational-wave detectors employ an optical resonator called an output mode-cleaner (OMC), which filters out junk light from the signal and the reference light, before it reaches the detection photodiode located at the asymm
etric port of the large-scale interferometer. The optical parameters of the OMC should be carefully chosen to satisfy the requirements to filter out unwanted light whilst transmitting the gravitational wave signal and reference light. The Japanese gravitational-wave detector KAGRA plans to use a very small amount of reference light to minimize the influence of quantum noise for gravitational waves from binary neutron stars, and hence the requirements to the OMC are more challenging than for other advanced detectors. In this paper, we present the result of numerical simulations, which verify that the OMC requirements are satisfied with the current design. We use the simulation program FINESSE and realistic mirror phase maps that have the same surface quality as the KAGRA test masses.
An optical cavity consisting of optically trapped mirrors makes a resonant bar that can be stiffer than diamond. A limitation of the stiffness arises in the length of the optical bar as a consequence of the finite light speed. High laser power and li
ght mass mirrors are essential for realization of a long and stiff optical bar that can be useful for example in the gravitational-wave detector aiming at the observation of a signal from neutron-star collisions, supernovae, etc. In this letter, we introduce a parametric signal amplification scheme that realizes the long and stiff optical bar without the need to increase the laser power.
Ground-based gravitational-wave detectors are based on high precision laser interferometry. One promising technique to improve the detectors sensitivity is the detuning of an optical cavity, which enhances the signal at around certain frequencies for
target astronomical sources. The detuning, however, involves technical noise due to an asymmetry of the control sidebands, which includes photo-detector noise and oscillator-phase noise. Here, we introduce a solution to reduce the two kinds of excess noise using an amplitude-modulation sideband that compensates the asymmetry. The solution is planned to be implemented in the Japanese second-generation gravitational-wave detector KAGRA.
Construction of the Japanese second-generation gravitational-wave detector KAGRA has been started. In the next 6 sim 7 years, we will be able to observe the space-time ripple from faraway galaxies. KAGRA is equipped with the latest advanced technolog
ies. The entire 3-km long detector is located in the underground to be isolated from the seismic motion, the core optics are cooled down to 20 K to reduce thermal fluctuations, and quantum non-demolition techniques are used to decrease quantum noise. In this paper, we introduce the detector configuration of KAGRA; its design, strategy, and downselection of parameters.
Reduction of coating thermal noise is a key issue in precise measurements with an optical interferometer. A good example of such a measurement device is a gravitational-wave detector, where each mirror is coated by a few tens of quarter-wavelength di
electric layers to achieve high reflectivity while the thermal-noise level increases with the number of layers. One way to realize the reduction of coating thermal noise, recently proposed by Khalili, is the mechanical separation of the first few layers from the rest so that a major part of the fluctuations contributes only little to the phase shift of the reflected light. Using an etalon, a Fabry-Perot optical resonator of a monolithic cavity, with a few coating layers on the front and significantly more on the back surface is a way to realize such a system without too much complexity, and in this paper we perform a thermal-noise analysis of an etalon using the Fluctuation-dissipation theorem with probes on both sides of a finite-size cylindrical mirror.
Thermal noise of a mirror is one of the limiting noise sources in the high precision measurement such as gravitational-wave detection, and the modeling of thermal noise has been developed and refined over a decade. In this paper, we present a derivat
ion of coating thermal noise of a finite-size cylindrical mirror based on the fluctuation-dissipation theorem. The result agrees to a previous result with an infinite-size mirror in the limit of large thickness, and also agrees to an independent result based on the mode expansion with a thin-mirror approximation. Our study will play an important role not only to accurately estimate the thermal-noise level of gravitational-wave detectors but also to help analyzing thermal noise in quantum-measurement experiments with lighter mirrors.
Thermal noise of a mirror is one of the most important issues in high precision measurements such as gravitational-wave detection or cold damping experiments. It has been pointed out that thermal noise of a mirror with multi-layer coatings can be red
uced by mechanical separation of the layers. In this paper, we introduce a way to further reduce thermal noise by locking the mechanically separated mirrors. The reduction is limited by the standard quantum limit of control noise, but it can be overcome with a quantum-non-demolition technique, which finally raises a possibility of complete elimination of coating thermal noise.
