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Spectral characterisation of half-wave plates for Cosmic Microwave Background B-mode studies

Braithwaite, Charlotte 2023. Spectral characterisation of half-wave plates for Cosmic Microwave Background B-mode studies. PhD Thesis, Cardiff University.
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Cosmic Microwave Background (CMB) experiments are pushing to measure the elusive signal within the polarised CMB, the primordial B-mode signal which, if detected, would prove cosmic inflation occurred in the early Universe, therefore, dedicated studies have been deployed to measure this signal. Polarisation modulators are typically used in these instruments to modulate the linear polarised CMB signals away from 1/f noises sources in the experiment, one commonly used is a Half Wave Plate (HWP). However, these devices introduce non-idealities into the scientific results, therefore it is imperative to measure their level of systematic errors before deploying the devices into the instrument. The research presented in this thesis is aimed at developing and comparing techniques used to characterise HWPs designed for Cosmic Microwave Background (CMB) experiments and propagate these results through to calculate scientific results; with a focus on the tensor-to-scalar ratio, r. The method and results for spectrally characterising an embedded metal mesh (EMM) HWP using a Vector Network Analyser (VNA) and a Fourier Transform Spectrometer (FTS) are compared and found to show that the use of both a FTS and VNA are critical to understanding the performance of a HWP over a large range of frequencies commonly used for CMB studies. It is also concluded that the performance of the EMM HWP shows these devices are useable for B-mode studies with their spectral transmission values and Mueller matrix components comparable to ones produced by Pancharatnam HWPs, while EMM HWPs are also shown to demonstrate a number of advantages compared to their Pancharatnam counterparts.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Physics and Astronomy
Subjects: Q Science > QC Physics
Uncontrolled Keywords: CMB, HWP, half wave plate, B mode, Pancharatnam, metal mesh
Funders: STFC
Date of First Compliant Deposit: 2 May 2024
Last Modified: 02 May 2024 11:12

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