Characterization of the terahertz near-field output of parallel-plate waveguides

Abstract

We experimentally characterize the field confinement properties of various parallel-plate waveguide (PPWG) geometries in the terahertz spectral range. In contrast to infinite-width PPWGs with free-space diffraction along the unshielded direction, finite-width (and also tapered) PPWGs show well-confined THz fields at the output facet. Both the transverse field component, perpendicular to the inside surfaces, and the longitudinal component, parallel to the propagation direction, exhibit strong lateral confinement. We also observe an antisymmetric longitudinal field distribution across the air gap, analogous to the symmetric surface plasmon polariton mode observed in optical slot waveguides.

Non-invasive terahertz field imaging inside parallel plate waveguides

“…The dip at z ¼ À0.15 mm has its origins in the interference between incident and reflected waves. The shape of the TPPWG structure can cause field enhancement in the proximity of the waveguide edges (propagating THz edge plasmons), 9 while the calculated value of E THz (t,z) is an integrated value of the THz electric field along the probe direction within the interaction volume. If additional freedom of the scanning stage movement along directions x and y is available, then edge enhancement effects can also be investigated using our method, with a transverse resolution determined by the Rayleigh range of the probe beam.…”

“…[2][3][4][5] Recently, a tapered parallel plate waveguide (TPPWG) has been proposed. [6][7][8] THz waves can be confined inside a TPPWG on subwavelength scale in both transverse dimensions, 9 thus enabling THz near-field spectroscopy with subwavelength resolution. The TPPWG also offers significant field enhancement and, thus, has a big potential for investigation of nonlinear THz phenomena with tabletop laser sources, which in recent years has become a very active research field.…”

THz-TDS using a photoconductive free-space linear tapered slot antenna transmitter

“…Here we focus on the design of a PC-FS-LTSA for near-field edge-coupled THz antenna excitation as an alternative to the standard HRFZ-Si lens. Figure 1 illustrates the PC-FS-LTSA which consists of a photoconductive active-area on SI-GaAs which is edge coupled to a metallic-slit based antenna [16][17][18][19][20][21] (i.e. the FS-LTSA).…”

Mode interference and radiation leakage in a tapered parallel plate waveguide for terahertz waves

“…Tapered parallel plate waveguides (PPWGs) have recently been proposed for confining terahertz (THz) pulses to sub-wavelength spatial dimensions with the aim of improving THz spectroscopy and imaging techniques. 1,2 THz pulse propagation without distortion is expected in the PPWG due to the formation of the dispersion-less transverse electro-magnetic (TEM) mode. 3 The assumption of single TEM mode propagation, however, may not hold true in some PPWG geometries.…”

“…The waveguide length of 29.4 mm was chosen to form the taper angle h recommended in the literature. 2 The guiding surfaces were polished with sub-micrometer grit lapping paper to minimize scattering losses during propagation. 9 A surface roughness of 30 nm was determined with an atomic force microscope by measuring the average deviation from the mean height in several regions along the waveguide.…”