149 research outputs found
Shot-noise-limited control-loop noise in an interferometer with multiple degrees of freedom
Precise measurements, such as those made with interferometric gravitational-wave detectors, require the measurement device to be properly controlled so that the sensitivity can be as high as possible. Mirrors in the interferometer are to be located at specific operation points to isolate laser noise and to accumulate the signal in resonant cavities. On the other hand, rigid control of an auxiliary degree of freedom may result in imposing sensing noise of the control on the target object as excess force noise. Evaluation of this so-called loop noise is important in order to design a decent control scheme of the measurement device. In this paper, we show the method to calculate the level of loop noise, which has been recently implemented in simulation tools that are broadly used for designing gravitational-wave detectors
Length sensing and control strategies for the LCGT interferometer
The optical readout scheme for the length degrees of freedom of the LCGT
interferometer is proposed. The control scheme is compatible both with the
broadband and detuned operations of the interferometer. Interferometer
simulations using a simulation software Optickle show that the sensing noise
couplings caused by the feedback control can be reduced below the target
sensitivity of LCGT with the use of feed forward. In order to improve the duty
cycle of the detector, a robust lock acquisition scheme using auxiliary lasers
will be used.Comment: 13 pages 9 figures. A proceedings paper for Amaldi9 conferenc
DECIGO and DECIGO pathfinder
A space gravitational-wave antenna, DECIGO (DECI-hertz interferometer Gravitational wave Observatory), will provide fruitful insights into the universe, particularly on the formation mechanism of supermassive black holes, dark energy and the inflation of the universe. In the current pre-conceptual design, DECIGO will be comprising four interferometer units; each interferometer unit will be formed by three drag-free spacecraft with 1000 km separation. Since DECIGO will be an extremely challenging mission with high-precision formation flight with long baseline, it is important to increase the technical feasibility before its planned launch in 2027. Thus, we are planning to launch two milestone missions. DECIGO pathfinder (DPF) is the first milestone mission, and key components for DPF are being tested on ground and in orbit. In this paper, we review the conceptual design and current status of DECIGO and DPF
Reduction and possible elimination of coating thermal noise using a rigidly controlled cavity with a QND technique
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 reduced 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
Local readout enhancement for detuned signal-recycling interferometers
Motivated by the optical-bar scheme of Braginsky, Gorodetsky and Khalili, we
propose to add to a high power detuned signal-recycling interferometer a local
readout scheme which measures the motion of the arm-cavity front mirror. At low
frequencies this mirror moves together with the arm-cavity end mirror, under
the influence of gravitational waves. This scheme improves the low-frequency
quantum-noise-limited sensitivity of optical-spring interferometers
significantly and can be considered as a incorporation of the optical-bar
scheme into currently planned second-generation interferometers. On the other
hand it can be regarded as an extension of the optical bar scheme. Taking
compact-binary inspiral signals as an example, we illustrate how this scheme
can be used to improve the sensitivity of the planned Advanced LIGO
interferometer, in various scenarios, using a realistic classical-noise budget.
We also discuss how this scheme can be implemented in Advanced LIGO with
relative ease
Photothermal effect in macroscopic optomechanical systems with an intracavity nonlinear optical crystal
Intracavity squeezing is a promising technique that may improve the
sensitivity of gravitational wave detectors and cool optomechanical oscillators
to the ground state. However, the photothermal effect may modify the occurrence
of optomechanical coupling due to the presence of a nonlinear optical crystal
in an optical cavity. We propose a novel method to predict the influence of the
photothermal effect by measuring the susceptibility of the optomechanical
oscillator and identifying the net optical spring constant and photothermal
absorption rate. Using this method, we succeeded in precisely estimating
parameters related to even minor photothermal effects, which could not be
measured using a previously developed method.Comment: 15 pages, 5 figure
Coating thermal noise 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 derivation 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.Comment: 13 pages, 4 figure
Double optical spring enhancement for gravitational-wave detectors
Currently planned second-generation gravitational-wave laser interferometers such as Advanced LIGO exploit the extensively investigated signal-recycling technique. Candidate Advanced LIGO configurations are usually designed to have two resonances within the detection band, around which the sensitivity is enhanced: a stable optical resonance and an unstable optomechanical resonance—which is upshifted from the pendulum frequency due to the so-called optical-spring effect. As an alternative to a feedback control system, we propose an all-optical stabilization scheme, in which a second optical spring is employed, and the test mass is trapped by a stable ponderomotive potential well induced by two carrier light fields whose detunings have opposite signs. The double optical spring also brings additional flexibility in reshaping the noise spectral density and optimizing toward specific gravitational-wave sources. The presented scheme can be extended easily to a multi-optical-spring system that allows further optimization
- …