Pollux test bench: from NUV to FUV polarimetric measurements

TL;DR

The paper describes the development of a specialized test bench for validating UV and FUV spectropolarimeters, crucial for the Pollux instrument on the HWO, aiming to enhance technology readiness and enable FUV polarimetry testing.

Contribution

It introduces an innovative vacuum-based test bench architecture for FUV spectropolarimeters, a first in the field, to validate their performance against stringent precision requirements.

Findings

Test bench design adaptable to different UV wavelengths

Validation methodology achieving $10^{-3}$ measurement precision

First development of FUV spectropolarimetry testing capability

Abstract

Pollux is a high-resolution spectropolarimeter proposed by an European consortium for HWO. The current design of Pollux features four spectropolarimetric channels, three of which are in the UV range. For the near-UV (NUV) [236-472 nm] and mid-UV (MUV) [118-236 nm] channels, the polarimeters consist of waveplates and prisms made of MgF2, a birefringent material. However, no such birefringent material can be used for the far-UV (FUV) channel [100-123 nm]. Therefore, the polarimeter for this FUV channel is composed solely of mirrors in an innovative assembly. In this talk, we aim to detail the architecture of the test bench that will allow us to validate the performance of these different polarimeters, as part of the HWO GOMaP. Given that we are working in the vacuum ultraviolet (VUV) range, the test bench operates in a vacuum chamber in a clean room. We will discuss the adaptable architecture of the bench based on wavelength and the measurement methodology that we will implement to test if the polarimeters achieve the precision of $10^{-3}$ required for the Pollux instrument. With this test bench, we will successfully increase the Technology Readiness Level (TRL) of UV spectropolarimeters and, for the first time, develop a means to test FUV spectropolarimetry.