Analogous to microsphere optical nanoscope, an easy and low-price method of THz imaging is proposed and developed for improving the spatial resolution beyond the diffraction limit. By attaching a 2-4 mm diameter Teflon sphere, a narrow, high-intensity, subdiffraction-waist THz beam with a strong jet-like distribution propagates into the background medium from the sphere’s shadow-side surface and a subwavelength spatial resolution better than λ/3 is demonstrated. Furthermore, the dielectric sphere-coupled THz microscope not only enables far-field, large-area measurement but also characterizes high-throughput and broad-band imaging properties. In addition, the size effect on terajet of dielectric sphere was simulated and shows that its magnification capability and focal length are size-dependent and frequencysensitive.
In this work, we demonstrate a high-selectivity terahertz (THz) band-stop filter with a wide range of center wavelengths (CWLs) from 150 to 600 μm (2.0 THz to 0.5 THz). The dip transmission is lower than 10 % at the center CWLs, even to 5 % at 1.9 THz. The band-stop terahertz filter is based on periodic metallic Cross Cell (CC) structures deposited on the top of a 50 μm thick polyimide film (Kapton) with low absorption and good mechanical properties, resulting in a large-area, freestanding and flexible membrane with a low intrinsic loss. The excellent tunable terahertz band-stop filter properties are investigated using terahertz time-domain spectroscopy. The measured and simulated results are coming to an excellent agreement. The THz band-stop filter possesses not only a light weight and polarization insensitivity but also a simple structure and high integration.
By using of high-resolution Terahertz time-domain spectroscopy, we show that both the fundamental and higher-order
Mie resonances can be excited in both magnetic and electric modes with in the one-dimensional dielectric grating.
Furthermore, their highly sensitive capability dependent on the frequency red-shift, line broadening, and transmission
decreasing were investigated with increasing refractive index and absorption strength of the surrounding media.
In order to provide a guide for the design and optimization of bowtie-shaped antenna arrays, their plasmonic properties have been experimentally and numerically investigated with emphasis on geometry and gap separation in THz frequencies. A stronger absorption, frequent red-shift and a higher Q-factor were observed in bowtie dimers, instead of the monomers. Based on the finite-element (FE) simulations using CST Microwave Studio, it was found that these resonant properties of the periodic bowtie particles can be further modulated by their geometric factors, including aspect ratio, area porosity as well as gap separation.
Terahertz time-domain spectroscopy was used to measure the optical properties of ZnO nanoparticles (NPs) in the
composite samples. The complex conductivity of pure ZnO NPs was extracted by applying Bruggeman effective medium
theory. We find that the real part of the complex conductivities increase with the increasing diameter of the ZnO NPs and
are governed by a restricted mean free path for NPs. The results demonstrate that carriers become localized with a
backscattering behavior in nano-structured ZnO.
The low-frequency optical properties of CuS nanoparticles in the composite samples were
measured by the terahertz time-domain spectroscopy. Then, the power absorption, refractive index,
complex dielectric function and conductivity of pure CuS nanoparticles are extracted by applying
Bruggeman effective medium theory. The measured dielectric function and conductivity are consistent with
the Lorentz theory of dielectric response as well as the Drude-smith model of conductivity in the frequency
range from 0.2 to 1.5 THz, respectively. In addition, the extrapolation of the measured data indicates that
the absorption is dominated by the lattice vibration localized at 4.7 ± 0.2 THz and the time constant for the
carrier scattering is only 64.3 fs due to increased electron interaction with interfaces and grain boundaries.
A simple wet-chemical route has been employed to synthesize β-ZnS nanoparticles with diameter of ca.15-20 nm. The
far-infrared characteristics of β-ZnS nanoparticles are investigated by terahertz time-domain spectroscopy (THz-TDS)
over the frequency range from 0.3 to 2.5 THz. The observed results show two obvious absorption features at 1.44 and
1.72 THz, which give rise to different vibration modes compared to the bulk ZnS. The theoretical calculation has been
carried out for better understanding the vibration behaviors by using of density functional theory (DFT) with
GAUSSIAN 03 software package. The simulated absorption spectrum was consistent with the experimental data. The
results reveal that the two absorption features are mainly ascribed to different vibration modes caused by the surface
A novel transmitted terahertz-emission microscopy (TTEM) is proposed and developed for improving the spatial
resolution of THz imaging. An epitaxial GaAs film grown on the GaP substrate was used as THz emitter; the transmitted
THz signal was collected and detected by a ZnTe electric-optical crystal. Because the thick of GaAs layer is merely 1 μm,
the THz wave source has the same size of the excited point. While attaching a sample directly onto the emitter, the
spatial resolution is decided by the diameter of focused pump beam, which can be achieved a few micrometers and
tunable. In addition, it can avoid the loss of the spectral components. By means of the near-field detection, the intensity,
spatial resolution and bandwidth of THz signal in this system can be enhanced further. The configuration and
characteristics of this microscopy are described in detail.