Abstract
The polarisation Sagnac speedmeter interferometer has the potential to replace the Michelson interferometer as the instrumental basis for future generations of ground-based gravitational wave detectors. The quantum noise benefit of this speedmeter is dependent on high-quality polarisation optics, the polarisation beam-splitter (PBS) and quarter-waveplate (QWP) optics that are key to this detector configuration and careful consideration of the effect of birefringence in the arm cavities of the interferometer. A PBS with an extinction ratio of better than 4000 in transmission and 700 in reflection for a 41° angle of incidence was characterised along with a QWP of birefringence of . The cavity mirror optics of a 10 m prototype polarisation Sagnac speedmeter were measured to have birefringence in the range 1 × 10−3 to 2 × 10−5 radians. This level of birefringence, along with the QWP imperfections, can be cancelled out by careful adjustment of the QWP angle, to the extent that the extinction ratio of the PBS is the leading limitation for the polarisation Sagnac speedmeter in terms of polarisation effects.
Highlights
Operational gravitational wave observatories, including the two LIGO detectors in the USA [1] and the Virgo detector in Italy [2] have been highly successful at measuring gravitational waves emitted by the coalescence of black-hole and neutron star binary systems [3, 4]
These detectors are based on Michelson interferometer configurations with suspended test masses where information about the relative position of the test masses is recovered from the phase of the laser light at the interferometer readout after the light has been modulated by interaction with a gravitational wave [5]
Imperfections in the polarisation optics will degrade the performance of the Sagnac speedmeter by reintroducing positional phase dependence into the output field and resulting in imperfect cancelation of quantum radiation pressure noise [21]
Summary
Operational gravitational wave observatories, including the two LIGO detectors in the USA [1] and the Virgo detector in Italy [2] have been highly successful at measuring gravitational waves emitted by the coalescence of black-hole and neutron star binary systems [3, 4] These detectors are based on Michelson interferometer configurations with suspended test masses where information about the relative position of the test masses is recovered from the phase of the laser light at the interferometer readout after the light has been modulated by interaction with a gravitational wave [5]. Sensitivity in the detectors upper frequency band, where quantum shot noise is the dominant effect, can be improved by increasing the laser power [8] and using squeezed light injection [9, 10] This comes at the penalty of increased quantum radiation pressure noise at lower frequencies, this currently remains below the classical noise level in this band. This make the polarisation Sagnac speedmeter attractive to consider as it is both conceptually straightforward and employs, for the most part, components and techniques that are already familiar in Michelsonbased detectors and has the advantage of linear arms that are compatible with existing and planned infrastructures
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