Characterisation of polarising components at cryogenic temperature

TL;DR

This study characterizes the polarization stability of key optical components at cryogenic temperatures, demonstrating minimal polarization distortion suitable for low-temperature optical spectroscopy applications.

Contribution

It provides the first detailed measurement of polarization properties of common optical components cooled to 4K, informing design of fiber-based cryogenic optical systems.

Findings

Polarization maintained within 10^-4 level from room temperature to 4K

Thermal contraction explains the polarization stability

Suitable for designing low-temperature fiber-optic probes

Abstract

Controlling polarisation directly at low temperature is crucial for development of optical spectroscopy techniques at sub-Kelvin temperatures, for example, in a hybrid scheme where light is fed into and collected in the cryostat by fibres that are as easy to install as electrical wiring, but where distortions in the fibre need to be compensated for by discrete polarising optical components. The latter are poorly characterised at low temperatures. So we cool-down polarising components from room temperature to 4K and monitor the evolution of the polarisation properties in this range. We test a zero-order half-wave plate, a polarising beamsplitting cube and a dichroic polariser in the optical telecommunication range at 1.5$\mu$m. We show that the polarisation is maintained at the $10^{-4}$ level within the whole temperature range. This is consistent with the typical thermal contraction of optical materials. This level of precision is sufficient for many optics experiments at low temperature. We argue that these experiments will allow the design of compact fibre based probes for cryogenic surfaces.