Digital notch filter

Filter determines whether time period of incoming signal matches time preset in filter. When signals do not match, high or low frequency deviation reading is displayed digitally

Quantum noise in laser-interferometer gravitational-wave detectors with a heterodyne readout scheme

We analyze and discuss the quantum noise in signal-recycled laser interferometer gravitational-wave detectors, such as Advanced LIGO, using a heterodyne readout scheme and taking into account the optomechanical dynamics. Contrary to homodyne detection, a heterodyne readout scheme can simultaneously measure more than one quadrature of the output field, providing an additional way of optimizing the interferometer sensitivity, but at the price of additional noise. Our analysis provides the framework needed to evaluate whether a homodyne or heterodyne readout scheme is more optimal for second generation interferometers from an astrophysical point of view. As a more theoretical outcome of our analysis, we show that as a consequence of the Heisenberg uncertainty principle the heterodyne scheme cannot convert conventional interferometers into (broadband) quantum non-demolition interferometers.Comment: 16 pages, 8 figure

Stripping and scrubbing of ammonium using common fractionating columns to prove ammonium inhibition during anaerobic digestion

Anaerobic digestion to produce biogas is generally considered as one of the most sustainable technologies for the production of renewable energy. During this microbial process, organically bound nitrogen is released as ammonium that ends up in the digestate and finally may inhibit the process. In this study, it is investigated if ammonium can be removed and recovered out of the liquid fraction of a thermophilic digestate from a potato processor. This is achieved at laboratory scale through an easy and self-designed stripping and scrubbing process using Vigreux and Dufton columns, which are commonly used laboratory fractionating columns. The stripping is performed at pH 8.5 and at 323.15K (50 degrees C), which results in the volatilization of the ammonium present in ammonia. Subsequently, the stripping gas charged with ammonia is put into contact with a sulphuric acid solution, resulting in (NH4)(2)SO4, which can be used as an N-S fertilizer. In addition, the digestion experiments have demonstrated that the biogas yield is 36% higher after removal of the ammonium from the digestate compared to the untreated digestate

Observing binary inspiral in gravitational radiation: One interferometer

We investigate the sensitivity of individual LIGO/VIRGO-like interferometers and the precision with which they can determine the characteristics of an inspiralling binary system. Since the two interferometers of the LIGO detector share nearly the same orientation, their joint sensitivity is similar to that of a single, more sensitive interferometer. We express our results for a single interferometer of both initial and advanced LIGO design, and also for the LIGO detector in the limit that its two interferometers share exactly the same orientation. We approximate the evolution of a binary system as driven exclusively by leading order quadrupole gravitational radiation. To assess the sensitivity, we calculate the rate at which sources are expected to be observed, the range to which they are observable, and the precision with which characteristic quantities describing the observed binary system can be determined. Assuming a conservative rate density for coalescing neutron star binary systems we expect that the advanced LIGO detector will observe approximately 69~yr${}^{-1}$ with an amplitude SNR greater than 8. Of these, approximately 7~yr${}^{-1}$ will be from binaries at distances greater than 950~Mpc. We explore the sensitivity of these results to a tunable parameter in the interferometer design (the recycling frequency). The optimum choice of the parameter is dependent on the goal of the observations, e.g., maximizing the rate of detections or maximizing the precision of measurement. We determine the optimum parameter values for these two cases.Comment: 40 pages (plus 7 figures), LaTeX/REVTEX3.0, NU-GR-

Sagnac Interferometer as a Speed-Meter-Type, Quantum-Nondemolition Gravitational-Wave Detector

According to quantum measurement theory, "speed meters" -- devices that measure the momentum, or speed, of free test masses -- are immune to the standard quantum limit (SQL). It is shown that a Sagnac-interferometer gravitational-wave detector is a speed meter and therefore in principle it can beat the SQL by large amounts over a wide band of frequencies. It is shown, further, that, when one ignores optical losses, a signal-recycled Sagnac interferometer with Fabry-Perot arm cavities has precisely the same performance, for the same circulating light power, as the Michelson speed-meter interferometer recently invented and studied by P. Purdue and the author. The influence of optical losses is not studied, but it is plausible that they be fairly unimportant for the Sagnac, as for other speed meters. With squeezed vacuum (squeeze factor $e^{-2R} = 0.1$) injected into its dark port, the recycled Sagnac can beat the SQL by a factor $\sqrt{10} \simeq 3$ over the frequency band 10 {\rm Hz} \alt f \alt 150 {\rm Hz} using the same circulating power $I_c\sim 820$ kW as is used by the (quantum limited) second-generation Advanced LIGO interferometers -- if other noise sources are made sufficiently small. It is concluded that the Sagnac optical configuration, with signal recycling and squeezed-vacuum injection, is an attractive candidate for third-generation interferometric gravitational-wave detectors (LIGO-III and EURO).Comment: 12 pages, 6 figure

Squeezed Light for the Interferometric Detection of High Frequency Gravitational Waves

The quantum noise of the light field is a fundamental noise source in interferometric gravitational wave detectors. Injected squeezed light is capable of reducing the quantum noise contribution to the detector noise floor to values that surpass the so-called Standard-Quantum-Limit (SQL). In particular, squeezed light is useful for the detection of gravitational waves at high frequencies where interferometers are typically shot-noise limited, although the SQL might not be beaten in this case. We theoretically analyze the quantum noise of the signal-recycled laser interferometric gravitational-wave detector GEO600 with additional input and output optics, namely frequency-dependent squeezing of the vacuum state of light entering the dark port and frequency-dependent homodyne detection. We focus on the frequency range between 1 kHz and 10 kHz, where, although signal recycled, the detector is still shot-noise limited. It is found that the GEO600 detector with present design parameters will benefit from frequency dependent squeezed light. Assuming a squeezing strength of -6 dB in quantum noise variance, the interferometer will become thermal noise limited up to 4 kHz without further reduction of bandwidth. At higher frequencies the linear noise spectral density of GEO600 will still be dominated by shot-noise and improved by a factor of 10^{6dB/20dB}~2 according to the squeezing strength assumed. The interferometer might reach a strain sensitivity of 6x10^{-23} above 1 kHz (tunable) with a bandwidth of around 350 Hz. We propose a scheme to implement the desired frequency dependent squeezing by introducing an additional optical component to GEO600s signal-recycling cavity.Comment: Presentation at AMALDI Conference 2003 in Pis

Laser-interferometer gravitational-wave optical-spring detectors

Using a quantum mechanical approach, we show that in a gravitational-wave interferometer composed of arm cavities and a signal recycling cavity, e.g., the LIGO-II configuration, the radiation-pressure force acting on the mirrors not only disturbs the motion of the free masses randomly due to quantum fluctuations, but also and more fundamentally, makes them respond to forces as though they were connected to an (optical) spring with a specific rigidity. This oscillatory response gives rise to a much richer dynamics than previously known, which enhances the possibilities for reshaping the LIGO-II's noise curves. However, the optical-mechanical system is dynamically unstable and an appropriate control system must be introduced to quench the instability.Comment: 7 pages, 3 figures; to appear in the Proceedings of 4th Edoardo Amaldi Conference on Gravitational Waves, Perth, Australia, 8-13 July 200

Experimental demonstration of a squeezing enhanced power recycled Michelson interferometer for gravitational wave detection

Interferometric gravitational wave detectors are expected to be limited by shot noise at some frequencies. We experimentally demonstrate that a power recycled Michelson with squeezed light injected into the dark port can overcome this limit. An improvement in the signal-to-noise ratio of 2.3dB is measured and locked stably for long periods of time. The configuration, control and signal readout of our experiment are compatible with current gravitational wave detector designs. We consider the application of our system to long baseline interferometer designs such as LIGO.Comment: 4 pages 4 figure