https://poggiolab.unibas.ch/full/2012PootPR.pdf

Mechanical systems in the quantum regime

Squeezed states of light and their applications in laser interferometers

Mechanical systems are ideal candidates for studying quantumbehavior of macroscopic objects. To this end, a mechanical resonator has to be cooled to its ground state and its position has to be measured with great accuracy. Currently, various routes to reach these goals are being explored. In this review, we discuss different techniques for sensitive position detection and we give an overview of the cooling techniques that are being employed. The latter include sideband cooling and active feedback cooling. The basic concepts that are important when measuring on mechanical systems with high accuracy and/or at very low temperatures, such as thermal and quantum noise, linear response theory, and backaction, are explained. From this, the quantum limit on linear position detection is obtained and the sensitivities that have been achieved in recent opto and nanoelectromechanical experiments are compared to this limit. The mechanical resonators that are used in the experiments range from meter-sized gravitational wave detectors to nanomechanical systems that can only be read out using mesoscopic devices such as single-electron transistors or superconducting quantum interference devices. A special class of nanomechanical systems are bottom-up fabricated carbon-based devices, which have very high frequencies and yet a large zero-point motion, making them ideal for reaching the quantum regime. The mechanics of some of the different mechanical systems at the nanoscale is studied. We conclude this review with an outlook of how state-of-the-art mechanical resonators can be improved to study quantum {\it mechanics}.

/pdf/mechanical-systems-in-the-quantum-regime-2g3p0kkzaq.pdf

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.

/pdf/the-geo-600-gravitational-wave-detector-2vs0980onw.pdf

The GEO 600 gravitational wave detector

We present a description of a system for automatic alignment of optical interferometers. The technique relies on using differential phase modulation to permit the detection of the phase difference between two fundamental-mode Gaussian beams at the output of an interferometer. Measurements of the spatially varying phase difference between the two beams by use of one or more multielement photodiodes permits information to be derived about the mismatch in overlap between the phase fronts at the output of the interferometer.

Automatic alignment of optical interferometers

Our development of a gravitational wave detector requires a Michelson interferometer of extreme sensitivity capable of measuring 10-16 m (i.e. some 10-10 of a wavelength λ of the illuminating laser light). Even after painstaking alignment of the interferometer components, and after considerable improvement of the laser stability, noise contributions much in excess of this goal were observed, due partly to fluctuations of the laser beam geometry. The two most obvious types of geometric beam fluctuations are a lateral beam jitter and a pulsation in beam width; these lead to spurious interferometer signals if the interfering wavefronts are misaligned in their tilts or in their curvatures respectively. The geometry of the laser beam can be considerably stabilized by passing it through an optical resonator. The geometric beam fluctuations, as viewed from this resonator, can be described by a well-centred ground mode TEMoo, contaminated by transverse modes TEM mn , with amplitudes decreasing rapidly with the mo...

A Mode Selector to Suppress Fluctuations in Laser Beam Geometry

The instrument described is used to locate and study various noise sources and other disturbances, which would restrict signal perceptibility. From an analysis of these disturbances, the demands on apparatus components are estimated. Some constructional details are given, as well as suggestions for improvement aimed at a future interferometer of increased base length, with the prospect of successful operation.

http://iopscience.iop.org/article/10.1088/0022-3735/12/11/010/pdf

An argon laser interferometer for the detection of gravitational radiation

Results of the Munich-Frascati gravitational-wave experiment

For the interferometric detection of extremely small displacements one of the principal limiting factors can be scattered light, having a certain path difference against the main beam, in combination with the inevitable frequency fluctuations of the light source. This paper presents a method to suppress the effect originating from the co-operation of these two deficiencies. The idea is to blot out the scattered light effect by deliberately phase-modulating the light with appropriate frequency and phase swing. A theoretical treatment is given for the principles of this novel method. The paper discusses possible sources of scattered light in a gravitational wave detector and the application of the method to blot out the effect caused by the scattered light. It furthermore describes a method to measure the different contributions of scattered light and presents first experimental results for their suppression. Suggestions and calculations for further improvements are given.

H. Billing

Papers

A Mode Selector to Suppress Fluctuations in Laser Beam Geometry

An argon laser interferometer for the detection of gravitational radiation

An argon laser interferometer for the detection of gravitational radiation

Results of the Munich-Frascati gravitational-wave experiment

A method to blot out scattered light effects and its application to a gravitational wave detector