Experimental investigation of the limitations of polarisation optics for future gravitational wave detectors based on the polarisation Sagnac speedmeter

The polarisation Sagnac speedmeter interferometer has the potential to replace Michelson as instrumental basis for future generations of ground-based gravitational wave detectors. quantum noise benefit this is dependent on high-quality optics, beam-splitter (PBS) and quarter-waveplate (QWP) optics that are key detector configuration careful consideration effect birefringence in arm cavities interferometer. A PBS with an extinction ratio better than 4000 transmission 700 reflection a $41^{\circ}$ angle incidence was characterised along QWP $\frac{\lambda}{4} + \frac{\lambda}{324}$. cavity mirror 10m prototype were measured have range $1\times10^{-3}$ $2\times10^{-5}$ radians. This level birefringence, imperfections, can be canceled out by adjustment angle, extent leading limitation terms effects.