The influence of substrate lens design in terahertz time-domain spectroscopy

Abstract

We describe measurements of the angular radiation patterns from lens-coupled terahertz antennas fabricated on photoconductive substrates. These measurements were performed with a novel terahertz (THz) timedomain spectrometer in which the femtosecond optical pulses used to gate the emitter and receiver antennas were delivered by optical fiber. We used this system to perform a comparison between the two substrate-lens designs commonly used in THz time-domain spectrometers. We measured both E-plane and H-plane emission patterns for a 90°bow-tie antenna. By comparing these experimental results with simulations based on Fresnel-Kirchoff diffraction, we find that the choice of substrate-lens design is important in determining not only the directivity of the emitted beam but also the spectral bandwidth. These results emphasize the significance of this crucial component in the design of broadband THz spectrometers.

Lens or resonator? Electromagnetic behavior of an extended hemielliptic lens for a sub‐millimeter‐wave receiver

“…Planar slot or strip elements combined with dielectric lenses are attractive building blocks for millimeter-and sub-millimeter-wave receivers [1][2][3][4][5]. The attention they have been attracting recently is due to their capability for compact integration with other electronic components, such as detecting diodes, local oscillators, and mixers.…”

“…On the other hand, the lens interface gives rise to reflections inside a realistic lens that may significantly affect the input impedance and sensitivity. This aspect, which has not been properly investigated in the literature, is a critical point in the overall design of lens antennas [2,5]. Various analytical techniques used to simulate dielectric lenses have been commonly based on ray tracing and neglecting the lens size and curvature, and hence have failed to characterize the internal resonances.…”

Focused terahertz waves generated by a phase velocity gradient in a parallel-plate waveguide

“…Conventional integrated THz transmitters are often equipped with silicon substrate lenses [9]. However, fixed components do not afford the possibility of dynamically changing the THz wave front in response to changing system needs.…”

Influence of terahertz waves on the fiber direction of CFRP composite laminates

“…The terahertz radiation is of critical importance in the spectroscopy evaluation of airport security screening, medical imaging, polar liquids, industrial systems and composites as well [1]. Also the terahertz time domain spectroscopy (TDz-TDS) is leading noncontact accurate detection of flaws and impact damages in composites, in which the TDz-TDS is based on photoconductive switches, which rely on the production of few-cycle terahertz pulses using a femtosecond laser to excite a photoconductive antenna [2][3][4][5]. This can generate sub-picosecond bursts of THz radiation, and subsequently detect them with high signal-to-noise.…”