K. D. Skeldon

The GEO 600 gravitational wave detector

The GEO 600 laser interferometer with 600 m armlength is part of a worldwide network of gravitational wave detectors. Due to the use of advanced technologies like multiple pendulum suspensions with a monolithic last stage and signal recycling, the anticipated sensitivity of GEO 600 is close to the initial sensitivity of detectors with several kilometres armlength. This paper describes the subsystems of GEO 600, the status of the detector by September 2001 and the plans towards the first science run.

An acoustic spanner and its associated rotational Doppler shift

Light carries a spin angular momentum associated with its polarization and an orbital angular momentum arising from its phase cross-section. Sound, being a longitudinal wave, carries no spin component but can carry an orbital component of angular momentum when endowed with an appropriate phase structure. Here, we use a circular array of loudspeakers driven at a common angular frequency ?s but with an azimuthally changing phase delay to create a sound wave with helical phase fronts described by exp?(i??). Such waves are predicted to have an orbital angular momentum to energy ratio of ?/?s. We confirm this angular momentum content by measuring its transfer to a suspended 60?cm diameter acoustic absorbing tile. The resulting torque on the tile (~6.1?10?6?Nm) is measured from observation of the motion for various torsional pendulums. Furthermore, we confirm the helical nature of the acoustic beam by observing the rotational Doppler shift, which results from a rotation between source and observer of angular velocity ?r. We measure Doppler shifted frequencies of ?s???r depending on the direction of relative rotation.

Development of high-resolution real-time sub-ppb ethane spectroscopy and some pilot studies in life science

We describe a high-resolution real-time spectroscopy system targeted to ethane gas with sensitivity > or = 70 ppt and response time from > or = 0.7 s. The measurement technique is based on a mid-IR lead-salt laser passing through a Herriott cell through which a gas sample flows. We compare wavelength scanning and locked configurations and discuss their relative merits. The technology has been motivated by clinical breath testing applications, ethane being widely regarded as the most important breath biomarker for cell damage via free-radical-mediated oxidative attack. We discuss preliminary human and animal studies in which ultrasensitive real-time ethane detection offers new diagnostic and monitoring potential.

Aspects of the suspension system for GEO 600

The GEO 600 gravitational wave detector is currently under construction in Germany. To ensure that the detector sensitivity is not limited by seismic noise above 50 Hz a significant degree of seismic isolation has to be provided for each test mass. To achieve this level of isolation each test mass, which will be made from fused silica (mass ∼14 kg), will be suspended as the final stage of a triple pendulum from an isolation stack consisting of layers of stainless steel masses and graphite loaded silicone rubber. Extending from the stack will be three cantilever springs supporting an upper mass from which a double pendulum stage will be suspended. This double pendulum will incorporate cantilever springs in the upper stage in order to enhance the vertical isolation, and will use fused silica fibers in the lower pendulum stage in order to minimize thermal noise from the pendulum modes. The expected performance from this arrangement of stacks, vertical spring stages, and double pendulums should achieve our go...

Portable optical spectroscopy for accurate analysis of ethane in exhaled breath

We report on a maintenance-free, ward-portable, tunable diode laser spectroscopy system for the ultra-sensitive detection of ethane gas. Ethane is produced when cellular lipids are oxidized by free radicals. As a breath biomarker, ethane offers a unique measure of such oxidative stress. The ability to measure real-time breath ethane fluctuations will open up new areas in non-invasive healthcare. Instrumentation for such a purpose must be highly sensitive and specific to the target gas. Our technology has a sensitivity of 70 parts per trillion and a 1 s sampling rate. Based on a cryogenically cooled lead-salt laser, the instrument has a thermally managed closed-loop refrigeration system, eliminating the need for liquid coolants. Custom LabVIEW software allows automatic control by a laptop PC. We have field tested the instrument to ensure that target performance is sustained in a range of environments. We outline the novel applications underway with the instrument based on an in vivo clinical assessment of oxidative stress.

The potential offered by real-time, high-sensitivity monitoring of ethane in breath and some pilot studies using optical spectroscopy

Breath analysis applied to biomedical applications has gained much momentum is recent years due to the growing research demonstrating that breath gas can provide clinically useful data. Particularly exciting is the area of real-time breath analysis which, when coupled with appropriately chosen target species, can offer a novel method for non-invasive patient monitoring. Here we describe the role of ethane, a breath gas of universal appeal in assessing in vivo oxidative stress (cell damage). We first present a review of emerging applications where real-time ethane monitoring could yield original new results for healthcare. We then report on results from a portable ethane spectroscopy system (accuracy better then 100 parts per trillion (1?part in 1010) over a 1?s time response) that we have developed to exploit some of these applications. By presenting some initial results from pilot studies in the life sciences, we comment on the requirements that the next stage of optical spectroscopy technology has to meet in order to benefit clinical end-users.

Dynamic study of oxidative stress in renal dialysis patients based on breath ethane measured by optical spectroscopy.

The application of optical spectroscopy for rapid accurate measurement of breath biomarkers has opened up new possibilities for monitoring and diagnostics in recent years. Here, we report on how our recent advances in optical detection of ethane have enabled us to record dynamic breath ethane patterns for patients undergoing kidney dialysis. Ethane is well established as a breath biomarker for free radical induced cell degradation. Moreover, renal dialysis is known to induce such oxidative attack, and our measurements may offer insight into the nature of this assault. Specifically, we have discovered that patients undergo significant breath ethane elevation at the beginning of each dialysis session. We have found an inverse relationship between the magnitude of this effect and number of months patients have been receiving treatment. We comment on how further refinements of our technology will allow a more detailed evaluation of the ethane elevation effect and ultimately lead to the assessment of potential interventions.

Oil and gas prospecting by ultra-sensitive optical gas detection with inverse gas dispersion modelling

We report a new oil and gas prospecting technique based on measurements of sub-part-per-billion ethane concentration in the atmosphere and local wind data. The sensitivity of our sensor enables detection, from a range of several km, of the naturally occurring ethane seepages that accompany hydrocarbon reservoirs. Using the concentration and wind data, the gas dispersion process is inverted to provide maps of surface ethane flux over several hundred km(2). Within a desert environment, we demonstrate the technique is capable of locating a controlled release and corresponds with the results from a geochemical soil sampling survey conducted over the same oil field.

Mode-cleaning and injection optics of the gravitational-wave detector GEO600

The British–German interferometric gravitational-wave detector GEO600 uses two high-finesse triangular ring cavities of 8 m optical pathlength each, as an optical mode-cleaning system. The modecleaner system is housed in an ultrahigh-vacuum environment to avoid contamination of the optics and to minimize both the influence of refractive index variations of the air and acoustic coupling to the optics. To isolate the cavities from seismic noise, all optical components are suspended as double pendulums. These pendulums are damped at their resonance frequencies at the upper pendulum stage with magnet-coil actuators. A suspended reaction mass supports three coils matching magnets bonded onto the surface of one mirror of each cavity, allowing length control of the modecleaner cavities to maintain resonance with the laser light. A fully automated control system stabilizes the frequency of the slave laser to that of the master laser, the frequency of the master laser to the length of the first modecleaner and the length of the first to the length of the second modecleaner. The control system uses the Pound–Drever–Hall sideband technique and operates autonomously over long time periods with only infrequent human interaction. The duty cycle of the system was measured to be 99.7% during an 18 day period. The throughput of the whole modecleaner system is about 50%. In this article, we give an overview of the mechanical and optical setup and the achieved performance of the double modecleaner system.

Effects of changes to the stable environment on the exhalation of ethane, carbon monoxide and hydrogen peroxide by horses with respiratory inflammation.

The aim of this study was to assess the effects of changes to the stable environment on exhaled markers of respiratory inflammation in six horses with clinical histories of recurrent airway obstruction. The horses were maintained for two weeks under conventional stable management (straw bedding and hay) and for two weeks on a reduced-dust regimen (paper bedding and ensiled grass), in a crossover study design. Exhaled ethane and carbon monoxide (CO) and exhaled breath condensate hydrogen peroxide (H2O2) were measured every three days under each regimen. The presence of clinical signs of airway inflammation (nasal discharge and cough) was monitored daily. The reduced-dust regimen was associated with fewer clinical signs of airway inflammation than the conventional regimen. Exhaled ethane and CO were significantly lower on the reduced-dust regimen and these markers were correlated with clinical signs of respiratory inflammation, but exhaled H2O2 was not affected by the management regimen.