Sensing and control in dual-recycling laser interferometer gravitational-wave detectors

We introduce length-sensing and control schemes for the dual-recycled cavity-enhanced Michelson interferometer configuration proposed for the Advanced Laser Interferometer Gravitational Wave Observatory (LIGO). We discuss the principles of this scheme and show methods that allow sensing and control signals to be derived. Experimental verification was carried out in three benchtop experiments that are introduced. We present the implications of the results from these experiments for Advanced LIGO and other future interferometric gravitational-wave detectors.     

Dual-recycled cavity-enhanced Michelson interferometer for gravitational-wave detection

The baseline design for an Advanced Laser Interferometer Gravitational-Wave Observatory (Advanced LIGO) is a dual-recycled Michelson interferometer with cavities in each of the Michelson interferometer arms. We describe one possible length-sensing and control scheme for such a dual-recycled, cavity-enhanced Michelson interferometer. We discuss the principles of this scheme and derive the first-order sensing signals. We also present a successful experimental verification of our length-sensing system using a prototype tabletop interferometer. Our results demonstrate the robustness of the scheme against deviations from the idealized design. We also identify potential weaknesses and discuss possible improvements. These results as well as other benchtop experiments that we present form the basis for a sensing and control scheme for Advanced LIGO.     

Experimental test of an alignment-sensing scheme for a gravitational-wave interferometer

An alignment-sensing scheme for all significant angular degrees of freedom of a power-recycled Michelson interferometer with Fabry-Perot cavities in the arms was tested on a tabletop interferometer. The response to misalignment of all degrees of freedom was measured at each sensor, and good agreement was found between measured and theoretical values.     

Twin mirrors for laser interferometric gravitational-wave detectors

Gravitational-wave detectors such as Virgo and the laser interferometric gravitational-wave observatory (LIGO) use a long-baseline Michelson interferometer with Fabry-Perot cavities in the arms to search for gravitational waves. The symmetry between the two Fabry-Perot cavities is crucial to reduce the interferometer's sensitivity to the laser amplitude and frequency noise. To this purpose, the transmittance of the mirrors in both cavities should be as close as possible. This paper describes the realization and the characterization of the first twin large low-loss mirrors with transmissions differing by less than 0.01%.     

High-gain power recycling of a Fabry-Perot Michelson interferometer for a gravitational-wave antenna

Power recycling was implemented on a fully suspended prototype interferometer with arm lengths of 20 m. A wave-front-sensing technique for alignment control of the suspended mirrors was also implemented, which allowed for several hours of stable operation. A power-recycling gain of greater than 12 was achieved, a significant increase over the highest gain in a suspended mirror Fabry-Perot Michelson interferometer reported to date.     

Signal extraction and optical design for an advanced gravitational-wave interferometer

We present an experimental demonstration of a locking and control scheme for an interferometer using a power-recycled resonant sideband extraction configuration and show that the measured response to mirror vibrations matches an optical model. We discuss some aspects of resonant sideband extraction that are relevant to gravitational-wave detection.     

Stability of a linear algorithm for signal observation in a gravitational-wave experiment

The sensitivity is discussed for a linear signal-detection algorithm resulting from change in the a priori information is a gravitational wave experiment.Translated from Izmeritel'naya Tekhnika, No. 9, pp. 3–4, September, 1995.     

Radiation pressure and stability of interferometric gravitational-wave detectors

The effect of radiation pressure on the stability of Fabry-Perot cavities with hanging mirrors is investigated. Such cavities will form an integral part of the laser interferometric gravitational-wave detectors that are being constructed around the globe. The mirrors are hung by means of a pendulum suspension and are locked by servo controls. We assume a realistic servo-control transfer function that satisfies the standard stability criteria. We find that for positive offsets from the resonance of the cavity the system is stable. However, we show that for negative offsets instabilities can occur, although the servo system has the effect of increasing the instability threshold, compared with the nonservoed case. Conditions for stability are finally given, involving the finesse of the cavity, the input power, the mass of the mirrors, the servo gain, and the phase detuning from perfect resonance. Gravitational-wave detectors with arm cavities having a finesse as low as approximately 200 could exhibit instabilities. Some implications for the locking of these detectors are finally given.     

Stability of giant Fabry-Perot cavities of interferometric gravitational-wave detectors

We consider the coupling of the thermoelastic mirror deformations to the resonance of giant cavities involved in interferometric detectors of gravitational waves. As this problem is coupled and nonlinear, instabilities could occur a priori. We analytically solve the coupled problem of thermoelastic deformations and their effect on the laser field, perturbatively, and we show that within the realm of our (physically reasonable) assumptions there are no instabilities that can simulate a false event in the observational frequency range of 1 Hz to 1 kHz.     

Information processing in a gravitational-wave experiment subject to pulse noise

We present a new algorithm for processing information in a gravitational-wave experiment; the algorithm is based on using Pearson curves to approximate the unknown probability density of the output noise of a gravitational antenna subject to chaotic pulse noise. Translated from Izmeritel'naya Tekhnika, No 5, pp. 3–7, May, 1999.     

Evaluation of prototype silicon drift detectors

Silicon drift detectors, of two elementary designs, have been fabricated and tested using β electrons and light pulses. Drift of electrons within the detectors has been observed over distances up to about 8 mm with high efficiency. Results are presented, some of which identify important design parameters of such devices.     

Glued detectors for the CRESST-II experiment

The Cryogenic Rare Event Search with Superconducting Thermometers Phase II (CRESST-II) at the L.N.G.S in Italy is searching for Dark Matter using low-temperature calorimeters. These detectors allow to discriminate different particles by simultaneous measurement of phonons and scintillation light. The sensors used consist of superconducting tungsten thin-film thermometers, which measure the thermal effect of the phonons created in an attached absorber crystal. It has been observed that the scintillation of the CaWO₄ absorber degrades during the process of depositing the tungsten film. In order to prevent this, a new technique for producing the detectors was investigated. This technique might also be valuable by expanding the range of scintillator materials suitable for producing a Dark Matter detector.     

Development of a dual-robot system for prototype production

A dual-robot machining system has been developed for manufacturing complex objects. The system consists of two six-axis industrial robots with flexible tool changers, a CAD/CAM package for geometric design and toolpath generation, a robot simulation package for collision avoidance, and a vision system for robot calibration. It offers the flexibility to reconfigure the robots of the system to accommodate workpieces of different shapes and sizes. A prototype of the system has been successfully developed and tested, and shows satisfactory performance in machining quality and control over the configurations of the robots. Examples are given of the application of the system to machining objects with spherical and sculptured surfaces. The system has been shown to be flexible, reconfigurable, automatic, and capable of manufacturing complex prototypes in the current industry environment.     

MAFL experiment: development of photonic devices for a space-based multiaperture fiber-linked interferometer

We present a three-telescope space-based interferometer prototype dedicated to high-resolution imaging. This project, named multiaperture fiber-linked interferometer (MAFL), was founded by the European Space Agency. The aim of the MAFL project is to propose, design, and implement for the first time to the best of our knowledge all the optical functions required for the global instrument on the same integrated optics (IO) component for controlling a three-arm interferometer and to obtain reliable science data. The coherent transport from telescopes to the IO component is achieved by means of highly birefringent optical fiber. The laboratory bench is presented, and the results are reported allowing us to validate the optical potentiality of the IO component in this frame. The validation measurements consist of the throughput of this optical device, the performances of metrological servoloop, and the instrumental contrasts and phase closure of the science fringes.     

Boron-coated straws as a replacement for He-based neutron detectors

US and international government efforts to equip major seaports with large area neutron detectors, aimed to intercept the smuggling of nuclear materials, have precipitated a critical shortage of ³He gas. It is estimated that the annual demand of ³He for US security applications alone is more than the worldwide supply. This is strongly limiting the prospects of neutron science, safeguards, and other applications that rely heavily on ³He-based detectors. Clearly, alternate neutron detection technologies that can support large sensitive areas, and have low gamma sensitivity and low cost must be developed.We propose a low-cost technology based on long copper tubes (straws), coated on the inside with a thin layer of ¹⁰B-enriched boron carbide (¹⁰B₄C). In addition to the high abundance of boron on Earth and low cost of ¹⁰B enrichment, the boron-coated straw (BCS) detector offers distinct advantages over conventional ³He-based detectors, and alternate technologies such as ¹⁰BF₃ tubes and ¹⁰B-coated rigid tubes. These include better distribution inside moderator assemblies, many-times faster electronic signals, no pressurization, improved gamma-ray rejection, no toxic or flammable gases, and ease of serviceability.We present the performance of BCS detectors dispersed in a solid plastic moderator to address the need for portal monitoring. The design adopts the outer dimensions of currently deployed ³He-based monitors, but takes advantage of the small BCS diameter to achieve a more uniform distribution of neutron converter throughout the moderating material. We show that approximately 63 BCS detectors, each 205 cm long, distributed inside the moderator, can match or exceed the detection efficiency of typical monitors fitted with a 5 cm diameter ³He tube, 187 cm long, pressurized to 3 atm.     

Design methodology for a Fabry-Perot interferometer used as a concentration sensor

We present the design methodology for a sensor that can nonintrusively monitor target gas concentration levels in a power plant exhaust flow. The measurement is based on radiative emission by rovibrational transitions that are well isolated from emission features of other constituents and requires both moderate spectral resolution (typically 1 nm or below) and relatively high optical throughput. A Fabry-Perot interferometer provides this capability, and its conceptual design is discussed at length. High-temperature radiative emission of nitric oxide in a background of water was used as a sample system for the design of a prototype Fabry-Perot interferometer. Predictions for the instrument are a minimum resolvable NO column density of 100 parts per million times meter based on a simple background subtraction scheme with a gas temperature of 800 K. Improved order sorting can dramatically lower this minimum. The prototype instrument was calibrated and tested with a laboratory simulator; results are presented and compared with predictions.     

Development of a low-noise analog front-end ASIC for CdTe detectors

This paper describes the recent development of a low-noise analog front-end ASIC for CdTe detectors. The ASIC is designed on the basis of the Open-IP LSI project led by JAXA and implemented using TSMC 0.35-μm CMOS technology. The ASIC contains eight identical channels, each of which includes a charge-sensitive amplifier, band-pass filters, and a sample-and-hold circuit. Preliminary testing of the ASIC achieved noise performance of 188e^-+7.5e^-/pF. In order to verify the low-noise characteristics, the ASIC was connected to a guard-ring-equipped CdTe diode detector with dimensions of and having a thickness of 0.5 mm. As a result, the gamma-ray spectra of radioactive sources were obtained with good energy resolutions of 2.51 and 2.35 keV (FWHM) for gamma rays of 59.5 and 122 keV, respectively, at room temperature.     

Silicon photomultipliers characterization for the EMR prototype of the MICE experiment

The SiPMs are excellent candidates for the replacement of PMTs in many experimental situations. In this article we describe the performances of different types of SiPMs from Hamamatsu and FBK-IRST before and after irradiation with photons and neutrons in terms of signal to noise ratio, time resolution and efficiency. The SiPMs are connected to a scintillation tracker/calorimeter, composed of eight layers (4x and 4y) of 10 scintillating bars each and have been tested at the CERN PS T9 beamline. The tracker/calorimeter is a small-size prototype of a bigger detector called EMR (Electron Muon Ranger), a particle identification system developed for the MICE experiment.