Article

Metal-mesh achromatic half-wave plate for use at submillimeter wavelengths

University of Manchester, School of Physics and Astronomy, Manchester, UK.
Applied Optics (Impact Factor: 1.78). 12/2008; 47(33):6251-6. DOI: 10.1364/AO.47.006251
Source: PubMed

ABSTRACT A metal-mesh achromatic half-wave plate (HWP) has been designed, manufactured, and tested for potential use in millimeter and submillimeter astronomical instruments. The prototype device presented here is based on a 12-grid Shatrow [IEEE Trans. Antennas Propag. 43, 109 (1995)] recipe to operate over the frequency range of 120-180 GHz. Transmission line modeling and finite-element analysis [Ansoft HFSS website: http://www.ansoft.com/hfss/] were used to optimize the design geometrical parameters in terms of the device transmission, reflection, absorption, phase-shift, and cross-polarization as a function of frequency. The resulting prototype device was constructed and characterized using incoherent radiation from a polarizing Fourier transform spectrometer to explore its frequency and polarization behavior. These measurements are shown to be in excellent agreement with the models. Lists of the achieved HWP performance characteristics are reported.

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    • "Figure 5. First broadband mesh-HWP made with free standing metal mesh grids (figures from [10]). Figure 6. Examples of modelling and measurements of an air-gap mesh-HWP (plots from [10]). "
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    • "This design uses capacitive and inductive metal-mesh geometries which each generate a frequency dependent phase shift with opposite sign. A first device fabricated from 6 capacitive grids and 6 inductive separated by air/vacuum gaps using accurately etched annular spacers demonstrated a bandwidth of 40 % (60 GHz) with a center frequency of 150 GHz [8]. Here we describe a procedure for optimizing the design of this type of HWP and present measurements of a device fabricated with a new process using dielectric spacers between the metallized sheets fused together with a hot pressing technique to make a solid self-supporting disc [9]. "
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    • "Components fabricated using this technique have been used in a number of THz cameras and spectrometers [5] [6] [7] [8] [9]. More recently, the same technique has been used to manufacture half-wave plates using aligned metallic patterns with air-gap spacing between the layers [10]. These traditional metal mesh components are not considered metamaterials because their electromagnetic properties are not independent of their thickness, i.e. they cannot be characterized as having a bulk electric permittivity and magnetic permeability. "
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