Polypropylene Embedded Metal-Mesh Broadband Achromatic Half Wave Plate for Millimeter Wavelengths

TL;DR

This paper presents a novel multi-layered metal mesh achromatic half wave plate designed for 125-250 GHz, optimized through simulations and tested in a spectrometer for astronomical polarimetry.

Contribution

It introduces a new multi-layered metal mesh design for broadband achromatic half wave plates in millimeter wavelengths, with fabrication and testing methods.

Findings

Performance aligns with models but shows lower differential phase shift.

Manufacturing imperfections likely cause phase shift discrepancies.

Prototype demonstrates potential for astronomical polarimetric applications.

Abstract

We describe a novel multi-layered metal mesh achromatic half wave plate for use in astronomical polarimetric instruments. The half wave plate is designed to operate across the frequency range from 125-250 GHz. The wave plate is manufactured from 12-layers of thin film metallic inductive and capacitive grids patterned onto polypropylene sheets, which are then bonded together using a hot pressing technique. Transmission line modelling and 3-D electromagnetic simulations are used to optimize the parameters of the metal-mesh patterns and to evaluate their optical properties. A prototype half wave plate has been fabricated and its performance characterized in a polarizing Fourier transform spectrometer. The device performance is consistent with the modelling although the measured differential phase shift for two orthogonal polarizations is lower than expected. This difference is likely to result from imperfect patterning of individual layers and misalignment of the grids during manufacture.