Birefringence-induced losses in interferometers

In interferometers one conceivable loss mechanism is depolarization of the light by inherent or thermally induced birefringence in optical substrates or coatings. The magnitude of this effect is determined quantitatively and compared with the losses due to thermal lensing

Analysis of a four-mirror cavity enhanced Michelson interferometer

We investigate the shot noise limited sensitivity of a four-mirror cavity enhanced Michelson interferometer. The intention of this interferometer topology is the reduction of thermal lensing and the impact of the interferometers contrast although transmissive optics are used with high circulating powers. The analytical expressions describing the light fields and the frequency response are derived. Although the parameter space has 11 dimensions, a detailed analysis of the resonance feature gives boundary conditions allowing systematic parameter studies

An investigation of eddy-current damping of multi-stage pendulum suspensions for use in interferometric gravitational wave detectors

In this article we discuss theoretical and experimental investigations of the use of eddy-current damping for multi-stage pendulum suspensions such as those intended for use in Advanced LIGO, the proposed upgrade to LIGO (the US laser interferometric gravitational-wave observatory). The design of these suspensions is based on the triple pendulum suspension design developed for GEO 600, the German/UK interferometric gravitational wave detector, currently being commissioned. In that detector all the low frequency resonant modes of the triple pendulums are damped by control systems using collocated sensing and feedback at the highest mass of each pendulum, so that significant attenuation of noise associated with this so-called local control is achieved at the test masses. To achieve the more stringent noise levels planned for Advanced LIGO, the GEO 600 local control design needs some modification. Here we address one particular approach, namely that of using eddy-current damping as a replacement or supplement to active damping for some or all of the modes of the pendulums. We show that eddy-current damping is indeed a practical alternative to the development of very low noise sensors for active damping of triple pendulums, and may also have application to the heavier quadruple pendulums at a reduced level of damping

Thermal lensing in recycling interferometric gravitational wave detectors

Thermal lensing limits the performance of advanced interferometric gravitational wave detectors that use high light powers. We evaluate the effects of thermal lensing in such systems and estimate their gravitational wave sensitivity assuming that fused silica optical substrates are employed. Although useful sensitivity can be achieved with established designs, the new technique of resonant sideband extraction is most promising for wideband detectors

Automatic beam alignment in the Garching 30-m prototype of a laser-interferometric gravitational wave detector

We describe a system for complete autoalignment of a suspended, power-recycled Michelson interferometer. All ten angular degrees of freedom are controlled by servo systems, thus ensuring optimal interference and fixing all beams in space. The methods and results are applicable to laser-interferometric gravitational wave detectors, and possibly also to other types of sensitive interferometers

Global Newtonian limit for the Relativistic Boltzmann Equation near Vacuum

We study the Cauchy Problem for the relativistic Boltzmann equation with near Vacuum initial data. Unique global in time "mild" solutions are obtained uniformly in the speed of light parameter $c \ge 1$. We furthermore prove that solutions to the relativistic Boltzmann equation converge to solutions of the Newtonian Boltzmann equation in the limit as $c\to\infty$ on arbitrary time intervals $[0,T]$, with convergence rate $1/c^{2-\epsilon}$ for any $\epsilon \in(0,2)$. This may be the first proof of unique global in time validity of the Newtonian limit for a Kinetic equation.Comment: 35 page

White matter changes and confrontation naming in retired aging national football league athletes

Using diffusion tensor imaging (DTI), we assessed the relationship of white matter integrity and performance on the Boston Naming Test (BNT) in a group of retired professional football players and a control group. We examined correlations between fractional anisotropy (FA) and mean diffusivity (MD) with BNT T-scores in an unbiased voxelwise analysis processed with tract-based spatial statistics (TBSS). We also analyzed the DTI data by grouping voxels together as white matter tracts and testing each tract's association with BNT T-scores. Significant voxelwise correlations between FA and BNT performance were only seen in the retired football players (p < 0.02). Two tracts had mean FA values that significantly correlated with BNT performance: forceps minor and forceps major. White matter integrity is important for distributed cognitive processes, and disruption correlates with diminished performance in athletes exposed to concussive and subconcussive brain injuries, but not in controls without such exposure

Resonant sideband extraction: a new configuration for interferometric gravitational wave detectors

We introduce a new Fabry-Perot based interferometric gravitational wave detector that, compared with previous designs, greatly decreases the amount of power that must be transmitted through optical substrates to obtain a given light power in its arms. This significantly reduces the effects of wavefront distortions caused by heating due to absorption in the optics, and allows an improved broadband sensitivity to be achieved

Experimental Demonstration of a Suspended Dual Recycling Interferometer for Gravitational Wave Detection

The advanced scheme of “signal recycling” is to be used in the British-German GEO 600 project, in addition to “power recycling” (which has become standard for all laser-interferometer gravitational wave detector projects). This combination, “dual recycling,” has been demonstrated for the first time on a fully suspended interferometer, the Garching prototype with 30 m arm length. Signal enhancement and power buildup were as predicted; operation was reliable, and a significant contrast enhancement was observed. A control system that can be extended to full scale gravitational wave detectors was employed