L. Schnupp

A Mode Selector to Suppress Fluctuations in Laser Beam Geometry

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...

An argon laser interferometer for the detection of gravitational radiation

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.

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

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.

The Munich Gravitational Wave Detector Using Laser Interferometry

In 1971, a small experimental group at Munich began with the development of a Weber-type resonant bar antenna for the detection of gravitational waves In coincidence experiments between Munich and Frascati (with the highest sensitivities achieved with room temperature bars) no events have been found [2]. As a possibility to improve the sensitivity by several orders of magnitude, work on laser interferometry was started in 1975 [3]. Pioneering work on this approach had been done by Forward [4] and Weiss [5].

The optics of an interferometric gravitational-wave antenna

The basic concept of an interferometric gravitational wave detector, the realization of the long light path with optical delay lines or with Fabry-Perot cavities, and the need for high light power are described. The techniques for improving the sensitivity, recycling and squeezed states of light, are considered and the consequences on the specifications of the optical components are shown. The specifications are explicitly given and particularly the influence of thermal effects is treated quantitatively.

Mechanical aspects in interferometric gravity wave detectors

In order to measure the tiny effects of gravitational waves, strains in space (i.e. relative changes in distance) of as little as 10-21 or even less have to be detected, at frequencies ranging from 10011z to several kHz. Large laser interferometers are the most promising approach to reach such extreme sensitivities. This ‘straightforward’ road is, however, obstructed by a multitude of effects that cause (or fake) such fluctuations in distance. Among these are seismic motions, thermal vibrations of optical components, pressure fluctuations of the residual gas in the vacuum tubes, and fundamental effects such as Heisenbergs uncertainty relation.

Reduction of noise due to scattered light in gravitational wave antennae by modulating the phase of the laser light

In long-light-path laser interferometry, as used for gravitational wave detection, scattered light is a major noise source. Interferometers that employ optical delay lines are particularly susceptible to noise from scattered light. The authors present a method of suppressing such noise signals by using fast phase modulation of the laser light. It is shown that all scattered all contributions from the delay line may be cancelled, up to arbitrarily long path differences. This can be achieved with an appropriately structured square-wave modulation function which switches the phase of the light by pi .

High Precision Laser Interferometry for Detection of Gravitational Radiation

The “First Generation” gravitational wave experiments, carried out in the 1970s, were not able to confirm definitely the existence of gravitational radiation. The strain sensitivity of these detectors was limited to δl/l ≃ 3·10−17. Estimates by astrophysicists suggest that a sensitivity about four orders of magnitude higher would be required for a realistic chance to detect gravitational waves [1].