A high power photodetection system for use with laser interferometric gravitational wave detectors

We report on an experiment to develop a high power, large bandwidth, infra-red photodetection system for use with radio frequency optical modulation schemes in the generation of gravitational wave detectors now being constructed. The incident light is split into 16 components by a configuration of 50:50 beam splitters and directed towards an array of InGaAs PIN photodiodes. The radio frequency output from the diodes is combined using ferrite loaded broad-band hybrid coaxial couplers together with coaxial transformers in a cascade, totem-pole, arrangement. The photodetection system has a very wide bandwidth, being shot noise limited to over 100 MHz in less than 150 mA of photocurrent. It has a photocurrent capability of up to 1.5 A which corresponds to an incident light power of about 2.3 W after optical losses are taken into account. The noise contribution from the photodiode array with bias applied is around 1.4 × 10<sup>-21</sup> W/Hz

Calibration of the Glasgow 10 m prototype laser interferometric gravitational wave detector using photon pressure

We show that the radiation pressure from an amplitude modulated, low power, Nd:YAG laser can be used to calibrate the displacement sensitivity of the Glasgow 10 m prototype gravitational wave detector. This demonstrates the possibility of radiation pressure being used as a standard method of calibrating long base line gravitational wave detectors. Further, this technique has the very important additional advantage that the test mass acted upon by the radiation pressure is not altered in any way, by, for example, the attachment of magnets, etc. The high Q-factor of the internal modes, required for good detector sensitivity, is therefore preserved

Exhaled ethane concentration in patients with cancer of the upper gastrointestinal tract - a proof of concept study

There has been growing interest in the measurement of breath ethane as an optimal non-invasive marker of oxidative stress. High concentrations of various breath alkanes including ethane have been reported in a number of malignancies. Our aim was to investigate the use of novel laser spectroscopy for rapid reporting of exhaled ethane and to determine whether breath ethane concentration is related to a diagnosis of upper gastrointestinal malignancy. Two groups of patients were recruited. Group A (n = 20) had a histo-pathological diagnosis of either esophageal or gastric malignancy. Group B (n = 10) was made up of healthy controls. Breath samples were collected from these subjects and the ethane concentration in these samples was subsequently measured to an accuracy of 0.2 parts per billion, ppb. Group A patients had a corrected exhaled breath ethane concentration of 2.3 ± 0.8 (mean ± SEM) ppb. Group B patients registered a mean of 3.1 ± 0.5 ppb. There was no statistically significant difference between the two groups (p = 0.39). In conclusion, concentrations of ethane in collected breath samples were not significantly elevated in upper gastrointestinal malignancy. The laser spectroscopy system provided a reliable and rapid turnaround for breath sample analysis

An upper limit to the frequency noise associated with the relaxation oscillation of a monolithic Nd:YAG ring laser

A measurement of the frequency noise at the relaxation oscillation frequency of a Nd:YAG monolithic non-planar ring laser is presented. By careful monitoring of various applied calibration signals, a limit to the frequency noise level of [similar to] 6.3 × 10-2 Hz/ root Hz is set over the relaxation oscillation bandwidth and it is shown that this is approximately at the level to be expected, based on the relaxation oscillation induced time varying refractive index

Narrow-band phase noise measurement around an electro-optically applied, RF phase modulation of a laser field

Light from a monolithic Nd:YAG non-planar ring oscillator laser was phase modulated using a low-phase-noise 12 MHz crystal oscillator driving a LiNbO3 electro-optic modulator. An upper limit to the additional amplitude spectral density of phase noise arising from the modulation process was measured to be 4 × 10-8 rad/ root Hz over an 800 Hz bandwidth around the modulation frequency. This noise is in addition to the intrinsic phase noise of the oscillator. This is significantly less than that required by the GEO 600 gravitational wave detector

Improved performance of the Glasgow 10 m prototype gravitational wave detector using an injection-locked Nd:YAG laser source

We present measurements of the displacement sensitivity from the Glasgow 10 m laser interferometric gravitational wave detector using an injection-locked Nd:YAG laser source; the type of laser system intended for use in some of the long-baseline observatories. The spectral density of displacement noise recorded above a few hundred Hz is ~4*10/sup -19/ m/ square root (Hz) which is close to the limit imposed by the shot noise for the optical properties of the system. This represents the best displacement sensitivity obtained with an injection locked Nd:YAG laser to date and provides evidence that close to shot noise limited performance can be obtained with such laser systems

Ultrahigh level of frequency stabilization of an injection locked Nd:YAG laser with relevance to gravitational wave detection

We report on measurements of the frequency noise of a highly stabilized injection locked Nd:YAG laser. We use a nested loop frequency stabilization scheme to achieve a loop gain of approximately 1×10<sup>6</sup> at Fourier frequencies around 1 kHz with frequency actuation applied only to the master oscillator. A frequency noise level of approximately 2×10<sup>-5</sup> HzHz<sup>-1/2</sup> was measured for the master laser around this frequency using an independent, narrow line width, suspended analyzer cavity. Furthermore we demonstrate that the frequency noise performance of the injection locked slave laser is identical to that of the master oscillator to this level. This performance is very close to the frequency noise specification for gravitational wave detection by GEO 600

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

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