Advanced Gravitational Wave Interferometric Detectors Research Articles

Resonant dampers for parametric instabilities in gravitational wave detectors

Advanced gravitational wave interferometric detectors will operate at their design sensitivity with nearly $\ensuremath{\sim}1\text{ }\text{ }\mathrm{MW}$ of laser power stored in the arm cavities. Such large power may lead to the uncontrolled growth of acoustic modes in the test masses due to the transfer of optical energy to the mechanical modes of the arm cavity mirrors. These parametric instabilities have the potential to significantly compromise the detector performance and control. Here we present the design of ``acoustic mode dampers'' that use the piezoelectric effect to reduce the coupling of optical to mechanical energy. Experimental measurements carried on an Advanced LIGO-like test mass have shown a tenfold reduction in the amplitude of several mechanical modes, thus suggesting that this technique can greatly mitigate the impact of parametric instabilities in advanced detectors.

Improved source localization with LIGO-India

A global network of advanced gravitational wave interferometric detectors is under construction. These detectors will offer an order of magnitude improvement in sensitivity over the initial detectors, and will usher in the era of gravitational wave astronomy. Gravitational wave sources can be localized on the sky, primarily through time of arrival measurements at the detectors, allowing for followup observations by telescopes. In this paper, we have evaluated the improvement in sky localization obtained by relocating one of the Advanced LIGO detectors to India.

Performance of a thermally deformable mirror for correction of low-order aberrations in laser beams

The thermally deformable mirror is a device aiming at correcting beam-wavefront distortions for applications where classical mechanical methods are precluded by noise considerations, as in advanced gravitational wave interferometric detectors. This moderately low-cost technology can be easily implemented and controlled thanks to the good reproducibility of the actuation. By using a flexible printed circuit board technology, we demonstrate experimentally that a device of 61 actuators in thermal contact with the back surface of a high-reflective mirror is able to correct the low-order aberrations of a laser beam at 1064 nm and could be used to optimize the mode matching into Fabry-Perot cavities.

On Special Optical Modes and Thermal Issues in Advanced Gravitational Wave Interferometric Detectors.

The sensitivity of present ground-based gravitational wave antennas is too low to detect many events per year. It has, therefore, been planned for years to build advanced detectors allowing actual astrophysical observations and investigations. In such advanced detectors, one major issue is to increase the laser power in order to reduce shot noise. However, this is useless if the thermal noise remains at the current level in the 100 Hz spectral region, where mirrors are the main contributors. Moreover, increasing the laser power gives rise to various spurious thermal effects in the same mirrors. The main goal of the present study is to discuss these issues versus the transverse structure of the readout beam, in order to allow comparison. A number of theoretical studies and experiments have been carried out, regarding thermal noise and thermal effects. We do not discuss experimental problems, but rather focus on some theoretical results in this context about arbitrary order Laguerre-Gauss beams, and other “exotic” beams.

Perspectives on beam-shaping optimization for thermal-noise reduction in advanced gravitational-wave interferometric detectors: Bounds, profiles, and critical parameters

Suitable shaping (in particular, flattening and broadening) of the laser beam has recently been proposed as an effective device to reduce internal (mirror) thermal noise in advanced gravitational-wave interferometric detectors. Based on some recently published analytic approximations (valid in the infinite-test-mass limit) for the Brownian and thermoelastic mirror noises in the presence of arbitrary-shaped beams, this paper addresses certain preliminary issues related to the optimal beam-shaping problem. In particular, with specific reference to the Laser Interferometer Gravitational-wave Observatory (LIGO) experiment, absolute and realistic lower bounds for the various thermal-noise constituents are obtained and compared with the current status (Gaussian beams) and trends (mesa beams), indicating fairly ample margins for further reduction. In this framework, the effective dimension of the related optimization problem, and its relationship to the critical design parameters are identified, physical-feasibility and model-consistency issues are considered, and possible additional requirements and/or prior information exploitable to drive the subsequent optimization process are highlighted.

Reducing thermal effects in mirrors of advanced gravitational wave interferometric detectors

We present an analytical model of temperature distribution, of thermal lensing and thermal distortion for a cylindrical mirror reflecting a large class of optical readout beams with a weak absorption rate in the coating. It is shown that non-traditional beam geometries could reduce the thermal lensing in the substrate and the thermal distortion of the surface by orders of magnitude.