Nanoscale dielectric grating polarizers tuned to 4.43 eV for ultraviolet polarimetry
L. RODRÍGUEZ DE MARCOS O. B. LEONG T. C. ASMARA S. P. HEUSSLER M. B. H. BREESE A. RUSYDI
L. RODRÍGUEZ DE MARCOS
T. C. ASMARA
S. P. HEUSSLER
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Abstract
Transmissive dielectric wire grid polarizers tuned to 4.43 eV (Mg II line, 280 nm), an important diagnostic line for solar physics, are presented in this communication. The polarizers are based on TiO2 gratings and designed with a period of ∼140 nm (7143 lines/mm), 40 nm line width (duty cycle of 0.286), and 100 nm line height. Several gratings are fabricated through electron beam lithography combined with reactive ion etching, whereby two parameters in the nanofabrication process are explored: e-beam dosage on the photoresist and TiO2 etching time. Polarization of samples is optically characterized using a spectroscopic ellipsometer in transmission mode, achieving the best result with an extinction ratio of ∼109 and a transmittance of 16.4% at the target energy of 4.43 eV. The shape of the gratings is characterized through atomic force microscopy (AFM) and scanning electron microscopy (SEM); the measured AFM profiles are distorted by the tip geometry, hence a simple deconvolution procedure is implemented to retrieve the real profile. By analysing the AFM and SEM profiles, we find that the real shapes of the different gratings are close to the design, but with a larger duty cycle than the intended value. With the real grating geometry, an improved model of the best sample was built with a finite-difference time-domain (FDTD) method that matches the result obtained through optical characterization.
Keywords
Electron beam lithography, Energy transfer, Extinction ratios, Magnetic fields, Scanning electron microscopy, Wire grid polarizers
Source Title
Optics Express
Publisher
OSA Publishing
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Date
2020-04-16
DOI
10.1364/OE.382839
Type
Article