Nanowire Grid Reflecting Polarizers for Ultraviolet Applications

Zhuan Zhao,Maria Guglielmina Pelizzo,Alain Jody Corso

doi:10.1109/jphot.2020.3031341

Zhuan Zhao, Maria Guglielmina Pelizzo + Show 1 more

Open Access

https://doi.org/10.1109/jphot.2020.3031341

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Abstract

Polarimetry in the far ultraviolet (FUV) is a powerful tool in many applications such as UV/EUV ellipsometry, characterization and control of the beam polarization status in large scale facilities and solar physics. FUV polarizers are among the most difficult components to manufacture, mainly due to the lack of dichroic and transparent materials in this spectral range. Although many different solutions for their fabrication have been investigated in the last decades, surprisingly, the use of Wire Grid Polarizers (WGPs) is still poorly investigated in this spectral region. In this work, two different concepts of WGPs have been designed and optimized for the FUV range: one is based on absorptive nano-wires on top of an highly reflective substrate, and the second one is based on highly reflective nano-wires on top of an absorptive substrate. Different wires’ shapes have been considered and relative structures optimized at a target wavelength of 121.6 nm. Two very promising solutions have been selected, which exhibit a polarization degree over 99.9% and a TE-reflectance over 0.2. Their sensitivity to the wires’ dimension parameters have been investigated to assess their feasibility.

Highlights

Polarimetry in the far-ultraviolet (FUV) and extreme-ultraviolet (EUV) wavelength range is a technique that has recently grown in importance in many fields of modern science, including FUV/EUV ellipsometry [1], characterization and control of the beam polarization in synchrotrons [2]–[4] and free-electron laser sources [2], [5]–[8], and solar physics [9], [10]
The electric field of the impinging beam is split into two components, the transverse electric (TE), which is oriented along the wires, and the transverse magnetic (TM), which is perpendicular to the wires
Designs A, C and G are the most promising structures in term of performance. All these structures have good performance in term of polarization factor P, the designs based on absorptive nano-wires (i.e., A, and C) give a lower TE-reflectance than those based on reflective nano-wires

Summary

Introduction

Polarimetry in the far-ultraviolet (FUV) and extreme-ultraviolet (EUV) wavelength range is a technique that has recently grown in importance in many fields of modern science, including FUV/EUV ellipsometry [1], characterization and control of the beam polarization in synchrotrons [2]–[4] and free-electron laser sources [2], [5]–[8], and solar physics [9], [10]. The bright lines in which the Hanle effect is evident are the HI Ly-α at 121.6 nm, the HI Ly-β at 102.5 nm, the HI Ly-γ at 97.2 nm and the OVI doublet at 103.2 nm and 103.8 nm [12] Considering these target lines, many examples of space missions with FUV polarimeters and spectro-polarimeters have been proposed, such as CLASP 1 [13], [14], SolmeX [15] and COMPASS [16]. MgF2 Wollaston prisms were proposed for astronomical polarimetry in the FUV [18] even if the relatively small deviation angles achievable ( 20◦) require the adoption of an instrumental geometry characterized by large optical paths and, small throughput. The WGPs are largely employed in the near ultraviolet (λ > 193 nm), visible and infrared [19], the extension to the FUV range, and in particular to the HI Ly-α line, is currently a challenge of the nanotechnology [20]

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