Near- and far-field measurements of phase-ramped frequency selective surfaces at infrared wavelengths

Abstract

Near- and far-field measurements of phase-ramped loop and patch structures are presented and compared to simulations. The far-field deflection measurements show that the phase-ramped structures can deflect a beam away from specular reflection, consistent with simulations. Scattering scanning near-field optical microscopy of the elements comprising the phase ramped structures reveals part of the underlying near-field phase contribution that dictates the far-field deflection, which correlates with the far-field phase behavior that was expected. These measurements provide insight into the resonances, coupling, and spatial phase variation among phase-ramped frequency selective surface (FSS) elements, which are important for the performance of FSS reflectarrays.

Real-Space Mapping of the Chiral Near-Field Distributions in Spiral Antennas and Planar Metasurfaces

“…To map the near-field distributions in chiral metal nanostructures, we apply interferometric s-SNOM. − It offers an excellent spatial resolution in the 10 nm range independently of the wavelength, operates in a wide spectral range including visible, infrared, and terahertz frequencies, and provides access to both the local near-field amplitude and phase, which enables the unambiguous recognition of localized antenna modes and propagating waveguide modes. Our s-SNOM setup (Figure ) is based on an atomic force microscope where commercial silicon tips (NanoWord, Arrow-NCR-50) were used to locally scatter the near-fields on the sample surface.…”

“…Here we demonstrate that the chiral near-field distributions in extended two-dimensional nanostructures can be mapped directly and in real space with scattering-type scanning near-field optical microscopy (s-SNOM) − employing circularly polarized illumination. We apply our technique to provide experimental evidence of the circular-polarization-sensitive nanofocusing capabilities of infrared Archimedean spiral nanoantennas in the near field, as a canonical example of chiral antenna structures.…”

Array truncation effects in infrared frequency selective surfaces

“…The interfering beams are sampled with a HgCdTe (MCT) detector, using a lock-in amplifier to sample the signal at the second-harmonic of the AFM tip dither frequency. The intensity at the detector can be expressed as follows [19,22,25…”

“…Here E scat is the field of the scattered sample beam, E ref is the field of the reference beam, φ is the phase difference between the two beams, and I b represents a background signal which is not related to either the sample signal or reference beam. The terms which do not oscillate according to φ are diminished significantly due to the use of the lock-in amplifier as well as the orthogonally polarized excitation and detection scheme [17,19,20,22,23,25]. In order to generate amplitude and phase images, several data sets are taken over the sample area of interest at different discrete reference phases.…”

“…The far-field measurements were carried out using an FTIR based ellipsometer in reflectivity mode, while the near-field measurements were made using scattering-scanning near-field optical microscopy (s-SNOM). Measurements of local electric field distributions using s-SNOM at mid-IR wavelengths have been shown recently for metamaterial samples [12,[17][18][19], as well as antennas [20][21][22], transmission lines [23,24], and phase-ramped structures [25]. The data presented in this report show the effects of truncation on the near-and far-field performance of a mid-IR metasurface by comparing the infinite array response with that of 11x11 arrays, 7x7 arrays, 3x3 arrays, and single square loops with a large periodicity.…”