Birefringence compensation method of test-mass substrates for gravitational wave detectors with arbitrary polarization states.

GW detectors are ultimately limited by thermal noise in their most sensitive region. Cryogenic operation combined with crystalline substrates and coatings is a promising approach to reduce this noise, thereby increasing their sensitivity and detection rate. However, crystalline materials can exhibit birefringent behaviors which will degrade the detector's sensitivity.

Correlation between birefringence and absorption mapping in large-size Sapphire substrates for gravitational-wave interferometry.

In high-sensitive laser interferometers, such as the gravitational-wave detector KAGRA, ultra-high-quality mirrors are essential. In the case of KAGRA, where cavity mirrors are cooled down to 20 K, large-size Sapphire crystals are used as the substrate for the main mirrors to achieve both a good optical quality (i.e.

Frequency-Dependent Squeezed Vacuum Source for Broadband Quantum Noise Reduction in Advanced Gravitational-Wave Detectors.

The astrophysical reach of current and future ground-based gravitational-wave detectors is mostly limited by quantum noise, induced by vacuum fluctuations entering the detector output port. The replacement of this ordinary vacuum field with a squeezed vacuum field has proven to be an effective strategy to mitigate such quantum noise and it is currently used in advanced detectors. However, current squeezing cannot improve the noise across the whole spectrum because of the Heisenberg uncertainty principle: when shot noise at high frequencies is reduced, radiation pressure at low frequencies is increased.