Speaker
Description
The low frequency Einstein Telescope (ET) is designed to operate at cryogenic temperatures and at a wavelength of 1550 nm. These new operating conditions, compared to current detectors, require the use of new materials, with silicon currently being the leading candidate for the main mirror substrates. However, possible birefringence in mirror substrates introduces additional contrast defect between the two interferometer arms, potentially limiting detector sensitivity. Meeting ET’s stringent optical requirements demands birefringence characterization at a level that remains a significant experimental challenge.
We present the ongoing development of a measurement system at Maastricht University designed to achieve this target. A birefringence map of a sample is obtained using a rotating quarter-wave plate, stepped from 0° to 180° in 2° increments while the transmitted p- and s-polarized intensities are recorded at each position. The measurement principle, the current status of the experimental setup, and the first results are presented. This work contributes to the qualification of silicon as a low-birefringence mirror material for the nextgeneration gravitational-wave detectors.