Matrix heater in the gravitational wave observatory GEO 600.

Large scale laser interferometric gravitational wave detectors (GWDs), such as GEO 600 require high quality optics to reach their design sensitivity. The inevitable surface imperfections, inhomogeneities, and light-absorption induced thermal lensing in the optics, can convert laser light from the fundamental mode to unwanted higher order modes, and pose challenges to the operation and sensitivity of the GWDs. Here we demonstrate the practical implementation of a thermal projection system which reduces those unwanted effects via targeted spatial heating of the optics. The thermal projector consists of 108 individually addressable heating elements which are imaged onto the beam splitter of GEO 600. We describe the optimization of the spatial heating profile and present the obtained results.

Abatement of thermal noise due to internal damping in 2D oscillators with rapidly rotating test masses.

Mechanical oscillators can be sensitive to very small forces. Low frequency effects are up-converted to higher frequency by rotating the oscillator. We show that for 2-dimensional oscillators rotating at frequency much higher than the signal the thermal noise force due to internal losses and competing with it is abated as the square root of the rotation frequency. We also show that rotation at frequency much higher than the natural one is possible if the oscillator has 2 degrees of freedom, and describe how this property applies also to torsion balances. In addition, in the 2D oscillator the signal is up-converted above resonance without being attenuated as in the 1D case, thus relaxing requirements on the read out. This work indicates that proof masses weakly coupled in 2D and rapidly rotating can play a major role in very small force physics experiments.

Effects of transients in LIGO suspensions on searches for gravitational waves.

This paper presents an analysis of the transient behavior of the Advanced LIGO (Laser Interferometer Gravitational-wave Observatory) suspensions used to seismically isolate the optics. We have characterized the transients in the longitudinal motion of the quadruple suspensions during Advanced LIGO's first observing run. Propagation of transients between stages is consistent with modeled transfer functions, such that transient motion originating at the top of the suspension chain is significantly reduced in amplitude at the test mass. We find that there are transients seen by the longitudinal motion monitors of quadruple suspensions, but they are not significantly correlated with transient motion above the noise floor in the gravitational wave strain data, and therefore do not present a dominant source of background noise in the searches for transient gravitational wave signals. Using the suspension transfer functions, we compared the transients in a week of gravitational wave strain data with transients from a quadruple suspension. Of the strain transients between 10 and 60 Hz, 84% are loud enough that they would have appeared above the sensor noise in the top stage quadruple suspension monitors if they had originated at that stage at the same frequencies. We find no significant temporal correlation with the suspension transients in that stage, so we can rule out suspension motion originating at the top stage as the cause of those transients. However, only 3.2% of the gravitational wave strain transients are loud enough that they would have been seen by the second stage suspension sensors, and none of them are above the sensor noise levels of the penultimate stage. Therefore, we cannot eliminate the possibility of transient noise in the detectors originating in the intermediate stages of the suspension below the sensing noise.

Effect of butyl 2-hydroxy-3-butynoate on sunflower leaf photosynthesis and photorespiration.

Detached leaves and whole plants of sunflower were supplied with butyl 2-hydroxy-3-butynoate (BHB), a competitive inactivator of glycolate oxidase, to evaluate the possibility of inhibiting photorespiration and increasing photosynthetic efficiency. In all treatments in vivo and in vitro, BHB inhibited glycolate oxidase. With partially purified glycolate oxidase from spinach leaves, the apparent K(i) for BHB was 13.2 micromolar.Low concentrations of BHB neither decreased photorespiration nor increased net photosynthesis. At higher concentrations, either a proportional decrease in photosynthesis and photorespiration or an inhibition of net photosynthesis greater than photorespiration was observed. CO(2) evolution in BHB-treated leaves was O(2)-sensitive and was derived from recent photosynthate. BHB inhibited photosynthesis in 2, 21, or 50% O(2) but the ratio of the rates of photosynthesis in these O(2) concentrations was the same as in control leaves. BHB treatment resulted in a stimulation of dark respiration.As photosynthesis, photorespiration, and dark respiration were all affected by BHB, the action of BHB on whole leaf metabolism appears to be complex. Substantial inhibition of photorespiration was accompanied by inhibition of photosynthesis and increases in photosynthesis were not observed.