Terahertz wave near-field compressive imaging with a spatial resolution of over λ/100.

We demonstrate terahertz (THz) wave near-field imaging with a spatial resolution of ∼4.5 µm using single-pixel compressive sensing enabled by femtosecond-laser (fs-laser) driven vanadium dioxide (VO2)-based spatial light modulator. By fs-laser patterning a 180 nm thick VO2 nanofilm with a digital micromirror device, we spatially encode the near-field THz evanescent waves. With single-pixel Hadamard detection of the evanescent waves, we reconstructed the THz wave near-field image of an object from a serial of encoded sequential measurements, yielding improved signal-to-noise ratio by one order of magnitude over a raster-scanning technique. Further, we demonstrate that the acquisition time was compressed by a factor of over four with 90% fidelity using a total variation minimization algorithm. The proposed THz wave near-field imaging technique inspires new and challenging applications such as cellular imaging.

Photoinduced active terahertz metamaterials with nanostructured vanadium dioxide film deposited by sol-gel method.

Applying the photoexcitation characteristics of vanadium dioxide (VO(2)), a dynamic resonant terahertz (THz) functional device with the combination of VO(2) film and dual-resonance metamaterial was suggested to realize the ultrafast external spatial THz wave active manipulation. The designed metamaterial realizes a pass band at 0.28-0.36 THz between the dual-resonant frequencies, and the VO(2) film is applied to control the transmittance of the spatial THz wave. More than an 80% modulation depth has been observed in the statics experiment, and the dynamic experimental results illustrate that this active metamaterial realizes up to a 1 MHz amplitude modulation signal loaded on a 0.34 THz carrier wave without any low noise amplified devices. The electromagnetic properties and photoinduced dynamic characteristics of this structure may have many potential applications in THz functional components, including modulators, intelligent switches, and sensors.

[The characteristics and dielectric dynamics of hydrated TiO2 in THz frequency range].

Terahertz time-domain spectroscopy (THz-TDS) was used to measure the information of water, the terahertz time-domain and frequency spectroscopy, absorbance, refractive index and the complex dielectric permittivity in the frequency range of 0.21-1 THz of various hydrated TiO2 samples with heating for different times. The result reveals that the absorbance of hydrated TiCO2 reduces with heating time increasing, and the location of the absorption peak is corresponded to the refractive index. The response of electric polarization in THz field has no clear relations with the frequency. With frequency increasing, the dielectric dissipation of hydrated TiO2 firstly decreases and then tends to be stable. The dielectric response always reduces with heating time increasing.

[Terahertz spectroscopic investigation of lanthanide-doped nano-TiO2].

Lanthanide-doped nano-TiO2 samples with different Ti/Ln (Ln = Ce, Nd, and Sm) were synthesized by sol-gel method. The samples were characterized by X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FTIR), X-ray photoelectron spectroscopy (XPS) and terahertz time-domain spectroscopy (THz-TDS). The results indicate that Ce, Nd, and Sm ions were uniformly dispersed into the TiO2; and the infrared activities of lanthanide-deped nano-TiO2 were much stronger than Undoped nano-TiO2, the refractive index of anatase TiO2 declines with frequency increasing in the frequency range of 0.2-1.70 THz at room temperature, and it exhibits anomalous dispersion. Unique characteristic absorption peaks at 1.35 and 1.58 THz were observed from Ce-doped nano-TiO2. Compared with undoped nano-TiO2, the absorption edges of Ce-doped nano-TiO2 were red-shifted remarkably and those of Nd and Sm ions doped nano-TiO2 were blue-shifted. Sm-doped nano-TiO2 has induced the least dielectric losses in the frequency range of 0.2-1.7 THz, and the average value is 0.05.